The sale of Wembley stadium will be opened up to other bidders in the autumn in a bid to flush out a higher offer than the £600 million on the table from Fulham owner Shahid Khan.

FA bosses have already been approached by at least three other potential buyers since the Standard last month revealed they have been in talks with the US billionaire, who also owns the Jacksonville Jaguars NFL franchise.

Although Mr Khan is said to be “in the box seat” in the negotiations, the FA team leading the talks are keen for the sale not to be seen as “a done deal”.

It is understood that the FA’s advisers, City investment bank NM Rothschild, have been instructed to “actively make it clear we are open to offers” after the summer. A higher price could allow more money to be ploughed back into grassroots football through new all-weather pitches and improvements to existing grass playing surfaces.

The Standard has also learned that:

Mr Khan originally offered just £200 million but was persuaded that the stadium was worth far more because of its potential for hosting an NFL franchise.

The FA will insist on a “golden share” type mechanism in any sale agreement so that it can block a resale to another owner thought to be an unsuitable custodian of the national stadium.

In pictures | The history of Wembley Stadium 75 show all In pictures | The history of Wembley Stadium 1/75 A general view of Wembley Stadium at night Getty Images 2/75 1923 The construction of Wembley Stadium Getty Images 3/75 1923 The construction of Wembley Stadium, circa 1923. First known as the Empire Stadium, it was built for the British Empire Exhibition Getty Images 4/75 1923 An aerial view of Wembley Stadium during the 1923 FA Cup Final between Bolton Wanderers and West Ham United Getty Images 5/75 1923 Mounted policemen control the crowds overflowing onto the pitch before the FA Cup Final between West Ham United and Bolton Wanderers at Wembley Stadium. It was the first final to be held at Wembley, with an estimated attendance of 200,000. The game became known as the 'White Horse Final' for the actions of PC George Scorey and his white horse Billy. Bolton Wanderers won the cup with a 2-0 victory Getty Images 6/75 1923 Putting up turnstiles for the West Ham United versus Bolton Wanderers Cup Final at Wembley Stadium Getty Images 7/75 1923 Crowds at the turnstiles before the FA Cup Final between West Ham United and Bolton Wanderers at Wembley Stadium Getty Images 8/75 1923 Crowds at the FA Cup Final between West Ham United and Bolton Wanderers scale the walls at Wembley Stadium Getty Images 9/75 1923 Police attempt to keep crowds off the pitch before of the first FA Cup Final at Wembley Stadium Getty Images 10/75 1923 King George V (1865 - 1936) and a huge crowd attend the first FA Cup Final to be held at Wembley Stadium Getty Images 11/75 1923 Players leap for the ball during the FA Cup Final between Bolton Wanderers and West Ham United Getty Images 12/75 1923 Groundsmen rolling the track in preparation for a British Legion rally at Wembley Stadium Getty Images 13/75 1924 Workmen strengthening the stands at Wembley Stadium Getty Images 14/75 1924 Bronco riding at a rodeo at Wembley Stadium Getty Images 15/75 circa 1924 World champion steer wrestler Buck Lucas astride his horse at a rodeo at Wembley stadium Getty Images 16/75 1925 Groundsmen mark out the touch line at Wembley Stadium Getty Images 17/75 1931 The Graf Zeppelin over Wembley stadium during a cup fina Getty Images 18/75 1932 A Post Office official testing out the phones to be installed at Wembley Stadium Getty Images 19/75 1932 Australian speedway champion Lionel Van Praag riding a motorcycle around the track at Wembley Stadium Getty Images 20/75 1934 The newly-constructed Empire Pool and Sports Arena at Wembley, next to Wembley stadium Getty Images 21/75 1936 Valuable racing greyhounds taking exercise in the grounds of Wembley Stadium Getty Images 22/75 1936 Workmen constructing the banking of the six-day cycle race track, in the car-park at Wembley Stadium Getty Images 23/75 1936 A stunt driver performs a car somersault at Wembley Stadium Getty Images 24/75 1938 A man conducts supporters' singing at Wembley Stadium before the start of a match between England and Scotland Getty Images 25/75 1938 Speedway racers at Wembley Getty Images 26/75 1938 Team Captain Gus Risman is chaired by team-mates with the trophy after Salford beat Barrow to win the Rugby League Challenge Cup at Wembley Stadium Getty Images 27/75 1939 Groundstaff at Wembley Stadium roll the pitch as part of the months of preparations for the FA Cup Final Getty Images 28/75 1942 England centre-forward Tommy Lawton heads the ball past Scotland's goalkeeper Dawson to score for England during an international match at Wembley Stadium on behalf of the Aid to Russia Fund Getty Images 29/75 1943 A baseball match between the US and Canadian Armies at Wembley Stadium Getty Images 30/75 1944 General Dwight D Eisenhower meeting the Chelsea team before the South Cup Final between Charlton Athletic and Chelsea at Wembley Stadium Getty Images 31/75 1947 Wembley Stadium during an international match between England and Scotland Getty Images 32/75 1948 Workmen resurfacing the track at Wembley Stadium, London, in preparation for the Olympic Games 33/75 1948 The opening day of the 14th Olympic Games at Wembley Stadium Getty Images 34/75 1948 A British athlete bears the Olympic Torch into the Empire Stadium at Wembley, London, and inaugurates the 1948 Olympic Games Getty Images 35/75 1948 British athlete John Mark carries the Olympic torch into Wembley Stadium at the opening ceremony of the 1948 Olympic Games Getty Images 36/75 1948 McDonald Bailey (number 35, centre) of Great Britain wins heat 6 of the Men's 100m event at Wembley Stadium during the London Olympics Getty Images 37/75 1948 Competitors in the men's 3000 metre steeplechase at the Olympic Games, Wembley Stadium Getty Images 38/75 1948 The start of the 1948 Olympic 800 metres final at Wembley Stadium Getty Images 39/75 1952 US Air Forces from England and Germany play one another at Wembley Stadium. The Fuerstenfeldbruck Eagles are seen gaining a touchdown against the Burtonwood Bullets Getty Images 40/75 1953 Blackpool's forward Stanley Matthews (left) dribbles past Bolton's midfielder Barass during the Cup Fnal on 03r May at Wembley stadium . Blackpool won 4-3 AFP/Getty Images 41/75 1960 King George V meeting the Arsenal team before the 1960 F A Cup final at Wembley Stadium Getty Images 42/75 1963 Cassius Clay (now Muhammad Ali) parades in the ring before his fight against Henry Cooper, in front of a 55,000 spectactors, wearing a red and gold dressing gown and crown. Getty Images 43/75 1963 Cassius Clay (Muhammad Ali), world heavyweight champion, is floored by British boxer heavyweight champion Henry Cooper during their fight at Wembley Stadium Getty Images 44/75 1965 Crowds listen with rapt attention to American evangelist Billy Graham's sermon at Wembley Getty Images 45/75 1966 England's 'no.1 supporter' Ken Bailey can be seen amongst the crowds at the World Cup Final match between England and West Germany at Wembley Stadium Getty Images 46/75 1966 Geoff Hurst scores England's third goal against West Germany in the World Cup final at Wembley Stadium Getty Images 47/75 1966 England captain Bobby Moore kissing the Jules Rimet trophy as the team celebrate winning the 1966 World Cup final against Germany at Wembley Stadium Getty Images 48/75 1968 Manchester United captain Bobby Charlton and manager Matt Busby celebrating their European Cup victory over Benfica at Wembley Stadium Getty Images 49/75 1972 A view of Wembley Stadium's twin towers from Olympic Way. Getty Images 50/75 1973 Wembley Stadium shown from the top of a 150 crane, used by the World of Sport TV camera Getty Images 51/75 1975 American motorcycle stunt rider Evel Knievel (1938 - 2007) attempts to jump 13 AEC Merlin buses at Wembley Stadium Getty Images 52/75 1975 American motorcycle stunt rider Evel Knievel (1938 - 2007) crashes on landing after jumping 13 AEC Merlin buses at Wembley Stadium Getty Images 53/75 1977 Scottish football fans, known as the Tartan Army, invading the pitch and pulling down goalposts after Scotland beat England 2-1 at Wembley Stadium Getty Images 54/75 1982 Pope John Paul II at Wembley Stadium 55/75 1981 Referee Keith Hackett reacts as Ricky Villa (c) of Spurs turns to celebrate after scoring the opening goal of the 1981 FA Cup Final Replay Tottenham Hotspur and Manchester City at Wembley Stadium Getty Images 56/75 1982 Live Aid concert PA 57/75 1988 Michael Jackson performs at Wembley 58/75 1990 American pop star Madonna performing to 74,000 fans at Wembley in 1990 wearing her famouse conical bra 59/75 1995 A general view of the supporters entering Wembley Stadium through the twin towers before the FA Cup Final between Manchester United and Everton at Wembley Stadium Getty Images 60/75 1996 A general view of Wembley Stadium, London Getty Images 61/75 1987 Denver Broncos in action during the American Bowl game against the Los Angeles Rams at Wembley Getty Images 62/75 1996 Paul Gascoigne celebrates in the 'Dentists Chair' with Steve McManaman, Teddy Sherringham (obscured) and Jamie Redknapp during their 1996 European Championships group stage match against Scotland at Wembley Stadium Getty Images 63/75 2003 The last few bricks of the famous Twin Towers are knocked down during it's redevolopment Getty Images 64/75 2007 England football manager Steve McClaren watches his team lose 3-2 to Croatia in a Group E Euro 2008 Qualifying game at Wembley AFP/Getty Images 65/75 2007 Miami Dolphins cheerleaders dance during the NFL American football match between the Miami Dolphins and the New York Giants at Wembley Stadium AFP/Getty Images 66/75 2007 An Aerial view of the new Wembley Stadium Getty Images 67/75 2011 The Bobby Moore statue outside Wembley Stadium Getty Images 68/75 2011 Lionel Messi of FC Barcelona in action against Rio Ferdinand and Wayne Rooney of Manchester United during the UEFA Champions League final between FC Barcelona and Manchester United FC at Wembley Stadium Getty Images 69/75 2011 Josep Guardiola manager of FC Barcelona is thrown in the air as Barcelona celebrate victory in UEFA Champions League final between FC Barcelona and Manchester United FC at Wembley Stadium Getty Images 70/75 2015 :The arch of London's Wembley Stadium is illuminated with the colours of the French national flag in tribute to the Paris terror attacks AFP/Getty Images 71/75 2017 Anthony Joshua vs Wladimir Klitschko Getty Images 72/75 2017 Anthony Joshua celebrates as Wladimir Klitschko lays on the floor during the IBF, WBA and IBO Heavyweight World Title bout at Wembley Stadium Getty Images 73/75 2017 Adele performs at Wembley Stadium Getty Images 74/75 2016 A general overview of action inside the stadium during the UEFA Champions League match between Tottenham Hotspur FC and AS Monaco FC at Wembley Stadium Tottenham Hotspur FC via Getty Images 75/75 2017 The Arsenal team celebrate with the FA Cup after The Emirates FA Cup Final between Arsenal and Chelsea at Wembley Stadium Getty Images 1/75 A general view of Wembley Stadium at night Getty Images 2/75 1923 The construction of Wembley Stadium Getty Images 3/75 1923 The construction of Wembley Stadium, circa 1923. First known as the Empire Stadium, it was built for the British Empire Exhibition Getty Images 4/75 1923 An aerial view of Wembley Stadium during the 1923 FA Cup Final between Bolton Wanderers and West Ham United Getty Images 5/75 1923 Mounted policemen control the crowds overflowing onto the pitch before the FA Cup Final between West Ham United and Bolton Wanderers at Wembley Stadium. It was the first final to be held at Wembley, with an estimated attendance of 200,000. The game became known as the 'White Horse Final' for the actions of PC George Scorey and his white horse Billy. Bolton Wanderers won the cup with a 2-0 victory Getty Images 6/75 1923 Putting up turnstiles for the West Ham United versus Bolton Wanderers Cup Final at Wembley Stadium Getty Images 7/75 1923 Crowds at the turnstiles before the FA Cup Final between West Ham United and Bolton Wanderers at Wembley Stadium Getty Images 8/75 1923 Crowds at the FA Cup Final between West Ham United and Bolton Wanderers scale the walls at Wembley Stadium Getty Images 9/75 1923 Police attempt to keep crowds off the pitch before of the first FA Cup Final at Wembley Stadium Getty Images 10/75 1923 King George V (1865 - 1936) and a huge crowd attend the first FA Cup Final to be held at Wembley Stadium Getty Images 11/75 1923 Players leap for the ball during the FA Cup Final between Bolton Wanderers and West Ham United Getty Images 12/75 1923 Groundsmen rolling the track in preparation for a British Legion rally at Wembley Stadium Getty Images 13/75 1924 Workmen strengthening the stands at Wembley Stadium Getty Images 14/75 1924 Bronco riding at a rodeo at Wembley Stadium Getty Images 15/75 circa 1924 World champion steer wrestler Buck Lucas astride his horse at a rodeo at Wembley stadium Getty Images 16/75 1925 Groundsmen mark out the touch line at Wembley Stadium Getty Images 17/75 1931 The Graf Zeppelin over Wembley stadium during a cup fina Getty Images 18/75 1932 A Post Office official testing out the phones to be installed at Wembley Stadium Getty Images 19/75 1932 Australian speedway champion Lionel Van Praag riding a motorcycle around the track at Wembley Stadium Getty Images 20/75 1934 The newly-constructed Empire Pool and Sports Arena at Wembley, next to Wembley stadium Getty Images 21/75 1936 Valuable racing greyhounds taking exercise in the grounds of Wembley Stadium Getty Images 22/75 1936 Workmen constructing the banking of the six-day cycle race track, in the car-park at Wembley Stadium Getty Images 23/75 1936 A stunt driver performs a car somersault at Wembley Stadium Getty Images 24/75 1938 A man conducts supporters' singing at Wembley Stadium before the start of a match between England and Scotland Getty Images 25/75 1938 Speedway racers at Wembley Getty Images 26/75 1938 Team Captain Gus Risman is chaired by team-mates with the trophy after Salford beat Barrow to win the Rugby League Challenge Cup at Wembley Stadium Getty Images 27/75 1939 Groundstaff at Wembley Stadium roll the pitch as part of the months of preparations for the FA Cup Final Getty Images 28/75 1942 England centre-forward Tommy Lawton heads the ball past Scotland's goalkeeper Dawson to score for England during an international match at Wembley Stadium on behalf of the Aid to Russia Fund Getty Images 29/75 1943 A baseball match between the US and Canadian Armies at Wembley Stadium Getty Images 30/75 1944 General Dwight D Eisenhower meeting the Chelsea team before the South Cup Final between Charlton Athletic and Chelsea at Wembley Stadium Getty Images 31/75 1947 Wembley Stadium during an international match between England and Scotland Getty Images 32/75 1948 Workmen resurfacing the track at Wembley Stadium, London, in preparation for the Olympic Games 33/75 1948 The opening day of the 14th Olympic Games at Wembley Stadium Getty Images 34/75 1948 A British athlete bears the Olympic Torch into the Empire Stadium at Wembley, London, and inaugurates the 1948 Olympic Games Getty Images 35/75 1948 British athlete John Mark carries the Olympic torch into Wembley Stadium at the opening ceremony of the 1948 Olympic Games Getty Images 36/75 1948 McDonald Bailey (number 35, centre) of Great Britain wins heat 6 of the Men's 100m event at Wembley Stadium during the London Olympics Getty Images 37/75 1948 Competitors in the men's 3000 metre steeplechase at the Olympic Games, Wembley Stadium Getty Images 38/75 1948 The start of the 1948 Olympic 800 metres final at Wembley Stadium Getty Images 39/75 1952 US Air Forces from England and Germany play one another at Wembley Stadium. The Fuerstenfeldbruck Eagles are seen gaining a touchdown against the Burtonwood Bullets Getty Images 40/75 1953 Blackpool's forward Stanley Matthews (left) dribbles past Bolton's midfielder Barass during the Cup Fnal on 03r May at Wembley stadium . Blackpool won 4-3 AFP/Getty Images 41/75 1960 King George V meeting the Arsenal team before the 1960 F A Cup final at Wembley Stadium Getty Images 42/75 1963 Cassius Clay (now Muhammad Ali) parades in the ring before his fight against Henry Cooper, in front of a 55,000 spectactors, wearing a red and gold dressing gown and crown. Getty Images 43/75 1963 Cassius Clay (Muhammad Ali), world heavyweight champion, is floored by British boxer heavyweight champion Henry Cooper during their fight at Wembley Stadium Getty Images 44/75 1965 Crowds listen with rapt attention to American evangelist Billy Graham's sermon at Wembley Getty Images 45/75 1966 England's 'no.1 supporter' Ken Bailey can be seen amongst the crowds at the World Cup Final match between England and West Germany at Wembley Stadium Getty Images 46/75 1966 Geoff Hurst scores England's third goal against West Germany in the World Cup final at Wembley Stadium Getty Images 47/75 1966 England captain Bobby Moore kissing the Jules Rimet trophy as the team celebrate winning the 1966 World Cup final against Germany at Wembley Stadium Getty Images 48/75 1968 Manchester United captain Bobby Charlton and manager Matt Busby celebrating their European Cup victory over Benfica at Wembley Stadium Getty Images 49/75 1972 A view of Wembley Stadium's twin towers from Olympic Way. Getty Images 50/75 1973 Wembley Stadium shown from the top of a 150 crane, used by the World of Sport TV camera Getty Images 51/75 1975 American motorcycle stunt rider Evel Knievel (1938 - 2007) attempts to jump 13 AEC Merlin buses at Wembley Stadium Getty Images 52/75 1975 American motorcycle stunt rider Evel Knievel (1938 - 2007) crashes on landing after jumping 13 AEC Merlin buses at Wembley Stadium Getty Images 53/75 1977 Scottish football fans, known as the Tartan Army, invading the pitch and pulling down goalposts after Scotland beat England 2-1 at Wembley Stadium Getty Images 54/75 1982 Pope John Paul II at Wembley Stadium 55/75 1981 Referee Keith Hackett reacts as Ricky Villa (c) of Spurs turns to celebrate after scoring the opening goal of the 1981 FA Cup Final Replay Tottenham Hotspur and Manchester City at Wembley Stadium Getty Images 56/75 1982 Live Aid concert PA 57/75 1988 Michael Jackson performs at Wembley 58/75 1990 American pop star Madonna performing to 74,000 fans at Wembley in 1990 wearing her famouse conical bra 59/75 1995 A general view of the supporters entering Wembley Stadium through the twin towers before the FA Cup Final between Manchester United and Everton at Wembley Stadium Getty Images 60/75 1996 A general view of Wembley Stadium, London Getty Images 61/75 1987 Denver Broncos in action during the American Bowl game against the Los Angeles Rams at Wembley Getty Images 62/75 1996 Paul Gascoigne celebrates in the 'Dentists Chair' with Steve McManaman, Teddy Sherringham (obscured) and Jamie Redknapp during their 1996 European Championships group stage match against Scotland at Wembley Stadium Getty Images 63/75 2003 The last few bricks of the famous Twin Towers are knocked down during it's redevolopment Getty Images 64/75 2007 England football manager Steve McClaren watches his team lose 3-2 to Croatia in a Group E Euro 2008 Qualifying game at Wembley AFP/Getty Images 65/75 2007 Miami Dolphins cheerleaders dance during the NFL American football match between the Miami Dolphins and the New York Giants at Wembley Stadium AFP/Getty Images 66/75 2007 An Aerial view of the new Wembley Stadium Getty Images 67/75 2011 The Bobby Moore statue outside Wembley Stadium Getty Images 68/75 2011 Lionel Messi of FC Barcelona in action against Rio Ferdinand and Wayne Rooney of Manchester United during the UEFA Champions League final between FC Barcelona and Manchester United FC at Wembley Stadium Getty Images 69/75 2011 Josep Guardiola manager of FC Barcelona is thrown in the air as Barcelona celebrate victory in UEFA Champions League final between FC Barcelona and Manchester United FC at Wembley Stadium Getty Images 70/75 2015 :The arch of London's Wembley Stadium is illuminated with the colours of the French national flag in tribute to the Paris terror attacks AFP/Getty Images 71/75 2017 Anthony Joshua vs Wladimir Klitschko Getty Images 72/75 2017 Anthony Joshua celebrates as Wladimir Klitschko lays on the floor during the IBF, WBA and IBO Heavyweight World Title bout at Wembley Stadium Getty Images 73/75 2017 Adele performs at Wembley Stadium Getty Images 74/75 2016 A general overview of action inside the stadium during the UEFA Champions League match between Tottenham Hotspur FC and AS Monaco FC at Wembley Stadium Tottenham Hotspur FC via Getty Images 75/75 2017 The Arsenal team celebrate with the FA Cup after The Emirates FA Cup Final between Arsenal and Chelsea at Wembley Stadium Getty Images

FA officials led by chief executive Martin Glenn are locked in detailed discussions with Mr Khan’s team about legal safeguards that will allay fears that the sale could leave English football locked out of its traditional home ground.

FA sources said the game’s governing body would need to be convinced that the stadium will remain the permanent “home of English football” available to host major England matches and tournament bid events. Other “non-negotiable” conditions include keeping a royal box, a “natural” playing surface and a capacity of at least 80,000. The FA must also be allowed to keep its headquarters at the stadium. Only after all the “rules of engagement” have been agreed and formalised will the FA move into “a more active process open to other bidders”, the sources said.

The approaches made since Mr Khan’s offer was made public have come from property and private equity companies and are not thought to be viable.

The FA makes almost all its money from its ownership of the stadium through its “Club Wembley” hospitality and corporate box business, which will not form part of the sale. The current value of its future stream of profits have been estimated at about £300 million.

In Pictures | Shahid Khan: Fulham FC and Jacksonville Jaguars Owner 11 show all In Pictures | Shahid Khan: Fulham FC and Jacksonville Jaguars Owner 1/11 Fulham Chairman Shahid Khan is greeted by fans in 2013 Getty Images 2/11 Getty Images 3/11 Jacksonville Jaguars owner Shahid Khan links arms with players before a Jacksonville Jaguars vs Baltimore Ravens NFL match at Wembley in 2017 Action Images via Reuters 4/11 Fulham Chairman Shahid Khan celebrates after Steve Sidwell scores their team's second goal during a Barclays Premier League match vs Crystal Palace at Selhurst Park in 2013 Getty Images 5/11 Mayor of London Sadiq Khan meets with Shahid Khan, owner of Fulham FC and the Jacksonville Jaguars, at his apartment in Chicago in 2016 PA 6/11 A Fulham fan meets Shahid Khan in 2013 PA 7/11 Shahid Khan holds his personalised Fulham FC Team shirt in 2013 Reuters 8/11 Shahid Khan at Craven Cottage in 2016 PA 9/11 Fulham's Owner and Chairman Shahid Khan applauds in the stands with Fulham CEO Alistair Mackintosh in 2014 PA 10/11 Fulham's chairman Shahid Khan celebrates following his team's 4-1 victory during the Barclays Premier League match between Crystal Palace and Fulham at Selhurst Park in 2013 Getty Images 11/11 Shahid Khan of the Jacksonville Jaguars walks on the sidelines during pregame against the Arizona Cardinals at University of Phoenix Stadium in 2017 Getty Images 1/11 Fulham Chairman Shahid Khan is greeted by fans in 2013 Getty Images 2/11 Getty Images 3/11 Jacksonville Jaguars owner Shahid Khan links arms with players before a Jacksonville Jaguars vs Baltimore Ravens NFL match at Wembley in 2017 Action Images via Reuters 4/11 Fulham Chairman Shahid Khan celebrates after Steve Sidwell scores their team's second goal during a Barclays Premier League match vs Crystal Palace at Selhurst Park in 2013 Getty Images 5/11 Mayor of London Sadiq Khan meets with Shahid Khan, owner of Fulham FC and the Jacksonville Jaguars, at his apartment in Chicago in 2016 PA 6/11 A Fulham fan meets Shahid Khan in 2013 PA 7/11 Shahid Khan holds his personalised Fulham FC Team shirt in 2013 Reuters 8/11 Shahid Khan at Craven Cottage in 2016 PA 9/11 Fulham's Owner and Chairman Shahid Khan applauds in the stands with Fulham CEO Alistair Mackintosh in 2014 PA 10/11 Fulham's chairman Shahid Khan celebrates following his team's 4-1 victory during the Barclays Premier League match between Crystal Palace and Fulham at Selhurst Park in 2013 Getty Images 11/11 Shahid Khan of the Jacksonville Jaguars walks on the sidelines during pregame against the Arizona Cardinals at University of Phoenix Stadium in 2017 Getty Images

Running football matches and other events such as rock concerts at Wembley currently makes only a small profit.

But this could be dramatically increased by boosting the number of event days by relocating an NFL franchise to London, the FA believes.

A spokesman for Mr Khan declined to comment, and the FA would not comment.