London: Former Australian foreign minister Alexander Downer has called on the North Atlantic Treaty Organisation (NATO) to scrap its regional roots and embrace new security partners such as Australia, South Korea and Japan.

His comments were made on the sidelines of the NATO Engages conference in Britain where leaders from the 29 member countries have gathered ahead of a meeting in Watford on Wednesday.

Queen Elizabeth II hosts NATO leaders on the 70th anniversary of the alliance during a reception at Buckingham Palace. Pool PA

Downer, who is also a former high commissioner to Britain, said the inclusion of non-European, non-American nations would strengthen the alliance.

"Because nowhere in this world today do Western countries get together in a way to co-ordinate security policy and NATO can be the catalyst to build a stronger, more global alliance of Western liberal democratic powers," he said.

He said the world was a very different place now, compared with 1949 when NATO was formed in the shadow of the World War II and in fear of Soviet Russia.

"We don't live in 1949, the world has completely changed," he said. "So what we would like to see is an outward-looking NATO, a NATO that not only embraces partners like Australia, Japan, Korea and the Indo-Pacific region but that NATO starts to think of itself more as the centrepiece of, if you like, very broadly defined Western security architecture."

Australia is a global partner of the organisation and former Labor prime minister Kevin Rudd appointed former Liberal leader Brendan Nelson to be Australia's first ambassador to it, based in Brussels, in 2012. The position is now held by career diplomat Justin Brown.

Former foreign minister Alexander Downer says the alliance should expand to include like-minded democracies. AAP

In excerpts from a speech he was set to deliver at the leaders' meeting on Wednesday, British Prime Minister Boris Johnson was set to reprise the motto made famous in popular culture by The Three Musketeers to underline NATO solidarity.

But his "one for all and all for one" rallying cry concealed discontent among member states over the alliance's purpose under Donald Trump's America First foreign policies, the ongoing row over funding.

Under NATO's principle of collective defence, the 29 member countries all regard an attack on one member as an attack on all. But Trump on Tuesday notably refused to say if the United States, under his presidency, would defend another member if it were attacked.

However Johnson ramped up talk of unity, describing it as a "giant shield of solidarity".

British Prime Minister Boris Johnson, pictured with the Queen, was keen to emphasise the solidarity of the alliance. PA

"Seventy years on, we are rock solid in our commitment to NATO and to the giant shield of solidarity that now protects 29 countries and nearly a billion people," Johnson is expected to say.

He will say as long as the nations of the alliance stand together, "no one could hope to defeat us - and therefore no one will start a war".

"If NATO has a motto, it is: One for all, and all for one. This doctrine of coming to one another’s aid, incarnated by NATO, provides the single most important explanation for why the British people and hundreds of millions of our friends live in peace and freedom today."

US President Donald Trump said that French President Emmanuel Macron had been "very insulting" by describing NATO as "brain dead" as the two leaders prepared to attend a NATO summit.

Johnson will also warn that "history shows that peace cannot be taken for granted and, even as we celebrate this anniversary, we must ensure that our deeds match our words."

Trump's ongoing campaign to enlist the NATO countries to commit to spending 2 per cent of GDP on defence, as Britain and the US do, was a major theme of his three media appearances totalling two hours on Tuesday. He chided Canada's Justin Trudeau for not spending enough.

Johnson avoided a politically risky one-on-one meeting with Trump, who clashed with his French counterpart Emmanuel Macron in extraordinary scenes on the day before the summit in London.

Johnson instead hosted Trump and other NATO leaders at 10 Downing Street after the Queen hosted the 29 heads of state at Buckingham Palace.

Johnson's rousing words disguised genuine soul-searching among NATO leaders about its purpose, given the US President's preference to shun multilateralism for his preference of one-on-one diplomacy aimed at boosting his election-winning America-First strategy.

Trump responded angrily to Macron's claims that the failure of US-leadership had caused NATO to suffer "brain death".

In a stunning role-reversal, Trump rushed to the defence of the alliance, which he once described as obsolete, saying Macron's descriptions were insulting.

Leaders are expected to agree on expanding NATO's definition of warfare to take in hostile activities in space and by hybrid methods, such as online disinformation and cyber attacks.