The Conservatives have refused to disclose the content of the election adverts they are targeting at voters in marginal seats over social media, raising concerns that Britain’s elections regulator is unable to properly scrutinise them.

Campaigners warn that the Electoral Commission is essentially blind when it comes to the ads because only the voters targeted by parties get to see them – unlike a billboard or television spot.

They also warn that the approach allows parties to put out “wildly different” and sometimes contradictory messages to different voters without being held to account for their discrepancies.

The Conservative party failed to respond to repeated requests by The Independent to disclose the content of the adverts they are micro-targeting at voters on Facebook and other social networks.

Labour did respond and provided a small number of adverts on request. The party however said it had over 1,200 different adverts and suggested it would be impractical to make all of them available.

The Electoral Commission says it is “live monitoring” the general election campaign and will report on any changes needed to the regulatory regime after the 8 June vote.

The content of adverts shown to voters is important because under Electoral Commission rules it determines whether spending on such campaigning should be marked as local or national.

UK General Election 2017 Show all 47 1 /47 UK General Election 2017 UK General Election 2017 12 June 2017 British Prime Minister Theresa May leaves 10 Downing Street for the 1922 committee on June 12, 2017 in London, England. British Prime Minister Theresa May held her first cabinet meeting with her re-shuffled team today Getty Images UK General Election 2017 12 June 2017 DUP leader Arlene Foster stands alongside deputy leader Nigel Dodds as they hold a press conference at Stormont Castle as the Stormont assembly power sharing negotiations reconvene following the general election on June 12, 2017 in Belfast, Northern Ireland. Discussions between the DUP and the Conservative party are also continuing in the wake of the UK general election as Prime Minister Theresa May looks to form a government with the help of the Democratic Unionist parties ten Westminster seats. Stormont and the political situation in Northern Ireland has been in limbo following the collapse of the power sharing executive due to the Renewable Heat Incentive scheme scandal which implicated the DUP Getty Images UK General Election 2017 12 June 2017 Priti Patel, International Development Secretary leaves 10 Downing Street Getty Images UK General Election 2017 12 June 2017 Larry the Downing Street cat runs ahead of Michael Fallon Britain's Secretary of State for Defence as he arrives for a cabinet meeting at Downing Street in London, Britain, June 12, 2017. REUTERS/Stefan Wermuth REUTERS UK General Election 2017 12 June 2017 Michael Gove, Environment Secretary leaves 10 Downing Street on June 12, 2017 in London, England. British Prime Minister Theresa May held her first cabinet meeting with her re-shuffled team today Getty Images UK General Election 2017 12 June 2017 Scottish National Party Leader Nicola Sturgeon (C) leaves after speaking to the media in Parliament Square. Getty Images UK General Election 2017 12 June 2017 British Prime Minister Theresa May (C, L) holds the first Cabinet meeting of her new team. Getty UK General Election 2017 11 June 2017 British Prime Minister Theresa May attends church in her constituency with her husband Philip May, a few days after disappointing results in a general election. Rex Features UK General Election 2017 9 June 2017 Leader of the Labour Party Jeremy Corbyn leaves Labour Party HQ this morning, following a general election yesterday. Parliament is hung, with no individual party gaining an overall majority. Post general election reaction. Rex UK General Election 2017 9 June 2017 BELFAST, NORTHERN IRELAND - JUNE 09: DUP leader and Northern Ireland former First Minister Arlene Foster (C) holds a brief press conference with the DUP's newly elected Westminster candidates who stood in the general election Getty Images UK General Election 2017 9 June 2017 A " Get May Out" demo took place opposite the gates of Downing Street, calling for May to resign, after the shock election results and Mays coalition with the DUP. Rex Features UK General Election 2017 9 June 2017 A demonstrator wears a mask depicting Britain's Prime Minister and leader of the Conservative Party Theresa May, poses with a mock gravestone bearing the words "Hard Brexit, RIP", during a protest photocall near the entrance 10 Downing Street in central London AFP/Getty Images UK General Election 2017 9 June 2017 Britain's Prime Minister Theresa May arrives at the Conservative Party's headquarters in London Reuters UK General Election 2017 9 June 2017 Britain's Prime Minister and leader of the Conservative Party Theresa May flanked by her husband Philip delivers a statement outside 10 Downing Street in central Londo Getty UK General Election 2017 9 June 2017 Britain's Prime Minister and leader of the Conservative Party Theresa May leaves Buckingham Palace in London the day after a general election in which the Conservatives lost their majority Getty Images UK General Election 2017 9 June 2017 A TV cameraman watches the door of 10 Downing Street in London Getty Images UK General Election 2017 9 June 2017 Labour leader Jeremy Corbyn is greeted by his Office Director Karie Murphy as he arrives at Labour Party HQ in Westminster, London, after he called on the Prime Minister to resign, saying she should 'go and make way for a government that is truly representative of this country' Dominic Lipinski/PA Wire UK General Election 2017 9 June 2017 Britain's Prime Minister Theresa May arrives at the Conservative Party's headquarters with her husband Philip in London REUTERS/Peter Nicholls UK General Election 2017 9 June 2017 Ukip leader Paul Nuttall speaks during a press conference at Boston West Golf Club where he announced that he is standing down as party leader Joe Giddens/PA UK General Election 2017 9 June 2017 Ruth Davidson, leader of the Scottish Conservatives, leaves the counting centre for Britain's general election with her partner Jen Wilson in Edinburgh, Scotland REUTERS/Russell Cheyne UK General Election 2017 9 June 2017 Scottish Labour leader Kezia Dugdale celebrates with candidate for Edinburgh South Ian Murray as he retains his seat at the Meadowbank Sports Centre counting centre in Edinburgh, Scotland Getty Images UK General Election 2017 9 June 2017 First Minister Nicola Sturgeon speaks to the media at the Emirates Arena in Glasgow, as counting is under way for the General Election Andrew Milligan/PA Wire UK General Election 2017 9 June 2017 Scottish Conservative leader Ruth Davidson at Meadowbank Sports Centre in Edinburgh, as counting is under way for the General Election PA UK General Election 2017 9 June 2017 Scottish National Party (SNP) leader Nicola Sturgeon reacts at the Emirates Arena in Glasgow, Scotland EPA UK General Election 2017 9 June 2017 Jeremy Corbyn, leader of Britain's opposition Labour Party, arrives at the Labour Party's Headquarters in London REUTERS/Marko Djurica UK General Election 2017 9 June 2017 UKIP Leader Paul Nuttall leaves in a car following the vote count for the constituency of Boston and Skegness in Boston, England Anthony Devlin/Getty Images UK General Election 2017 9 June 2017 British Prime Minister and Conservative Party leader Theresa May speaks at the declaration at the election count at the Magnet Leisure Centre in Maidenhead, England. Getty Images UK General Election 2017 8 June 2017 A policer officer enters a polling station in London AP UK General Election 2017 8 June 2017 A woman leaves after casting her vote at the Hove Museum and Art Gallery near Brighton, in southern England Getty UK General Election 2017 8 June 2017 A polling station sign is seen on a telephone box outside the polling station at Rotherwick Hall, west of London Getty UK General Election 2017 7 June 2017 A woman walks past a general election display in the window of a betting shop in Camden on June 7, 2017 in London, United Kingdom. Britain goes to the polls tomorrow, Getty Images UK General Election 2017 7 June 2017 Britain's Prime Minister Theresa May visits Atherley Bowling Club during an election campaign visit on June 7, 2017 in Southampton, England. Britain goes to the polls tomorrow June 8 to vote in a general election. Getty Images UK General Election 2017 6 June 2017 A supporter wears a pair of Jeremy Corbyn decorated tights at a general election campaign event in Birmingham, central England, on June 6, 2017. Britain goes to the polls on June 8 to vote in a general election only days after another deadly terror attack in the nation's captial. AFP/Getty Images UK General Election 2017 6 June 2017 A picture taken in London, shows election leaflets from various parties displayed ahead of the United Kingdom's general elections. Britain goes to the polls on June 8 to vote in a general election only days after another terrorist attack on the nation's capital AFP/Getty Images UK General Election 2017 6 June 2017 Election workers, George Gaunt and Luca Tragid deliver the first ballot boxes, on the Royal Mile in Edinburgh AFP UK General Election 2017 6 June 2017 British Prime Minister Theresa May meets with Conservative party supporters during an election campaign visit to a bakery during an election campaign visit on June 6, 2017 in Fleetwood, north-west England. Britain goes to the polls on June 8 to vote in a general election only days after another terrorist attack on the nation's capital Getty Images UK General Election 2017 5 June 2017 British Prime Minister Theresa May speaks during a general election campaign visit to a removals depot in Edinburgh AFP/Getty Images UK General Election 2017 3 June 2017 Pro-Independence supporters hold a march through Glasgow AFP/Getty Images UK General Election 2017 3 June 2017 Opposition Labour Party leader Jeremy Corbyn campaigns for the upcoming general election in Beeston, Nottinghamshire AFP/Getty Images UK General Election 2017 3 June 2017 Labour leader Jeremy Corbyn reacts to supporters after a rally at Beeston Youth and Community Centre as he visits the East Midlands during the final weekend of the General Election campaign on June 3, 2017 in Nottingham, England. If elected in next week's general election Mr Corbyn is pledging to create a million new jobs and to scrap zero-hours contracts Getty Images UK General Election 2017 1 June 2017 Scottish Conservative and Unionist Party leader Ruth Davidson joins a selection of Scottish Conservative election candidates and activists during campaigning on May 1, 2017 in South Queensferry, Scotland. With only seven days to go until the general election on June 8th, polls are showing the SNP out in front and the Conservatives set to close in on Labour. Getty Images UK General Election 2017 29 May 2017 Prime Minister Theresa May canvasses in Richmond with Conservative candidate Zac Goldsmith on May 29, 2017 in London, United Kingdom. After suffering defeat in the London Mayoral election Zac Goldsmith resigned over the Government's position on Heathrow expansion. He stood as an Independent but lost in a by-election to the Liberal Democrats. Britain goes to the polls on June 8 to elect a new parliament in a general election Getty Images UK General Election 2017 22 May 2017 Liberal Democrat leader Tim Farron poses for a selfie taken by carer April Preston during a General Election campaign visit to the Barlow Medical Centre, in Didsbury, Manchester Yui Mok/PA UK General Election 2017 22 May 2017 Britain's Prime Minister Theresa May speaks at an election campaign event in Wrexham, Wales Reuters UK General Election 2017 22 May 2017 Britain's main opposition Labour Party leader Jeremy Corbyn, and Labour's former deputy Prime Minister, John Prescott, exit the party's general election campaign 'battle' bus as they arrive at an event in Kingston upon Hull, northern England Getty Images UK General Election 2017 22 May 2017 Britain's main opposition Labour Party leader Jeremy Corbyn walks with supporters between venues, before speaking again at another general election campaign event in Kingston upon Hull, northern England Getty Images UK General Election 2017 22 May 2017 An anti-fox hunting protester is taken away and arrested by police outside the venue where Britain's Prime Minister Theresa May was due to launch the Welsh Conservative general election manifesto at Gresford Memorial Hall in the village of Gresford, near Wrexham, North Wales, on May 22, 2017. Britain goes to the polls on June 8 to elect a new parliament in a general election AFP/Getty Images

Adverts that only promote political parties’ national messages are allowed to be registered as national spending – with more relaxed spending limits – even if they are targeted to a specific area.

But if local issues or candidates are named in such adverts then their cost must be registered as local candidate spending – with strict limits put in place to stop money from deciding elections.

Alexandra Runswick, director of Unlock Democracy, said: “Political parties targeting voters on social media during general elections is not a new issue, and yet our electoral law has failed to catch up. Rather than being able to rely on an independent body to monitor election spending – to make sure all parties are playing by the rules – it has once again been left to the public and campaigners to hold parties to account.

“Social media advertising is targeted at individuals using private online accounts and therefore by its very nature is harder to police than the more traditional campaign communications, like billboards and newspaper adverts. But we know that parties have spent and are spending money on targeted online advertising – in the 2015 general election alone, the Conservatives spent £1.2m on Facebook campaigns, while Labour spent over £16k.

“Parties should of course be able to use these platforms to reach potential voters, but the Electoral Commission also needs to be equipped to monitor how parties are spending their money. Otherwise, we simply don’t know whether they are making accurate reports.

“At the moment, too many loopholes exist for parties to exploit. Are parties, for example, declaring targeted social media adverts in local candidates’ budgets? Without urgent reform, a new election expenses scandal may be on the horizon.”

Katie Ghose, the chief executive of the Electoral Reform Society (ERS), said: “Digital campaigning can be a good thing, but the kind of micro-targeting we’re seeing raises serious questions about transparency. We have no idea who or how the parties are going after voters.

“And unlike public billboards or TV broadcasts, social media targeting is ‘for your eyes only’ – something that can enable parties to pedal widely different messages without being held to account.

Theresa May wants to change the internet with new regulations

“This is just the latest trend of something that is rife in our politics. The ERS has found that campaigns spend 22 times as much money in the most competitive constituencies compared to the safest seats.

“That looks likely to be replicated when it comes to the new digital micro-targeting. So in many ways, this is nothing new – it’s an extension of a voting system that leads parties to go after a handful of people in marginal seats rather than speaking to all voters.”

At general elections local candidates can spend only £8,700 plus either 6p or 9p per registered parliamentary voter in their seat, depending on the type of constituency. Nationally, limits are far more relaxed, with parties allowed to spend £30,000 per seat, usually a total of around £19m for nationwide parties.

The latest episode comes days after the Information Commissioner’s Office launched an inquiry into the misuse of personal data by election campaigns when it comes to targeting voters.

The Information Commissioner, Elizabeth Denham, said last week there was “data protection risks” from new methods and reminded parties of “the need to comply with the law” during elections.

A spokesperson for the Electoral Commission said: “Whether a cost should be accounted for at a local or national level is dependent on who the particular activity is seeking to promote. Our guidance explains that candidates need to make an honest and reasonable assessment as to whether the costs of campaign activity were for their election or whether they were for promoting the national party.