London mayor Sadiq Khan has slammed Boris Johnson and Donald Trump as 'extreme right wing leaders' and claimed that the lessons of the Second World War are in 'danger of being forgotten' because of their rise in popularity.

Khan labelled the US president 'the global poster-boy for white nationalism' and said that he inspired right wing leaders around the world, including the Prime Minister and Nigel Farage.

The London mayor added that support for democracy in the western world is at a 'record low'.

He also believes that Brexit Party leader Farage has pushed Johnson and his Conservative party to become 'ever more right wing, illiberal and intolerant'.

Sadiq Khan believes right-wing populism is on the rise and believes the lessons of the Second World War in danger of being forgotten

The mayor wrote in the Observer, : 'For the first time in more than 70 years, it seems the lessons of the second world war are genuinely at risk of being forgotten or, worse still, being rewritten.

'The EU and NATO, so instrumental in preventing another bloody world war, are facing unprecedented attacks – often from leaders of the very nations that helped create them.

'Support for democracy is at a record low across the western world, and the values that define liberal democracies are under siege – from the rule of law and the independence of the judiciary, to a free press and a vibrant civil society.'

Commenting on Johnson's controversial decision to shut down parliament for five weeks before the October 31 Brexit deadline, Khan said: 'Just last week we saw the disdain Boris Johnson has for parliament and our democracy.'

The London mayor said the success of Hungary's Viktor Orbán, Matteo Salvini in Italy and Marine Le Pen in France are examples of extremist far-right politicians achieving success and eroding democracy.

Khan labelled US president Donald Trump 'the global poster-boy for white nationalism'

The London mayor said that Brexit Party leader Nigel Farage had pushed Johnson and his Conservative party to become 'ever more right wing, illiberal and intolerant'

He believes that Trump, and his daily attacks on the press and judiciary, is to blame for the spread of this right-wing populism in the world.

It is the latest chapter in a long-standing enmity between the London mayor and the US president.

Khan compared Trump's language to that of 'a 20th century fascist' and accused him of 'shamelessly' interfering in the Conservative party leadership race, ahead of the US President's three-day State visit to the UK in June.

It is the latest chapter in a long-standing enmity between the London mayor and the US president as shown in these tweets from June

Trump in return mocked Khan for being a 'stone cold loser' and the mayor's office immediately fired back, saying Trump was offering 'childish insults which should be beneath the President of the United States'.

Trump also said that Khan had done a 'terrible job' as London mayor.

He added that the mayor should concentrate on tackling crime in London, rather than attacking the leader of the United States.