Boris Johnson suggested Andy Burnham is lying about Russian influence on the EU referendum today - as No10 desperately backtracked on the PM's claim. 

Mr Burnham declared in a podcast that he had been told 'clearly' on arriving in No10 that Vladimir Putin had meddled in the 2016 vote.

It is thought to be the first time a premier has publicly declared there was foreign influence on the process - and caused a storm of protests from Brexiteers.

But within hours Downing Street had to clarify that the Russian interference had not been successful, stressing that the Government believes the result was 'legitimate'.

'Given everything we know about Russia, it is inconceivable they did not seek to use the referendum to their benefit,' the official spokesman said.

'But... we do not believe they have succeeded.'

The spokesman added: 'The PM accepts the referendum result, he is not looking back he is looking to the future.' 

He declined to confirm that Mr Burnham had been shown specific evidence of interference. 

In a furious response to the interference claim this afternoon, Mr Johnson - who led the Brexit campaign - said: 'This is just not true. 

'As soon as I became foreign secretary I asked the security services the same question and they replied that there was no evidence of any successful interference in the 2016 referendum, by Russia or any other power. 

'Either the security services have changed their view - which would be very odd - or Burnham is lying about what he has been told. 

'After all Starmer was in power for two years and had access to exactly the same information.' 

The Tories accused Mr Burnham of 'spreading conspiracy theories about the Brexit referendum'.

Nigel Farage told a press conference: 'The Prime Minister is a liar.... there was no Russian interference and the Russia hoax runs all the way through this.'

Mr Burnham later insisted he hadn't questioned the legitimacy of the 2016 EU referendum with his podcast comments.

Tory leader Kemi Badenoch, challenging the PM in the Commons, said he had 'implied that the referendum result was illegitimate because of Russian interference'.

But the PM replied: 'I implied no such thing in my comments on The Rest Is Politics podcast. I think she should go back and look again.'

He also said 'it is a matter of record that Russian actors sought to interfere' in a previous general election, adding: 'We think it is inconceivable that this was the first time.'

Earlier one of Mr Burnham's own ministers had seemed to be trying to walk back the remarks. 

Foreign minister Stephen Doughty told LBC: 'We know what the result was. I don't think they've succeeded in their efforts to undermine our elections.'

He added: 'The security minister's been very clear that they've attempted but not succeeded, in his evidence that he gave previously on this.

'But the fact is that they are attempting to interfere, and we all need to be alert to that and respond accordingly.'

The latest row erupted when Mr Burnham made claims about Russian interference during an appearance on The Rest is Politics podcast.

Mr Burnham said he had spoken to German Chancellor Friedrich Merz about the influence of Russia during a visit to Berlin last week.

'There is certainly misinformation, disinformation that is emanating from Russia into German politics,' he said.

'But I asked the question coming to Downing Street: was there interference in the 2016 referendum from Russia? And I've had the clear answer that yes, there was.

'I mean, these things are important now to put clearly on the record and help voters in Germany and France understand that some of this politics is instigated via our enemies, namely Russia.'

Mr Burnham said the UK had been 'too much on the back foot' and as a result voters had not been 'informed sufficiently about the extent to which people are seeking to disrupt the political process from overseas'.

The muddle came as Mr Burnham prepares to reignite Brexit wars in the Commons, after suggesting he could support rejoining the EU.

The PM made a statement to MPs this afternoon arguing that cutting ties with Brussels has not 'delivered what was promised'.

He teed up a summit with the EU next month, saying failing to seek closer relations would be a 'dereliction of duty'.

Last week Mr Burnham used his conference speech to reopen the issue of EU membership, despite vowing before taking over from Keir Starmer that he would not.

Mr Burnham told Europhile party activists that he wanted to explore 'options' including committing to rejoin in the next election manifesto. He refused to say whether there would need to be another referendum.

Ahead of the Commons returning this afternoon, a No10 source said: 'Andy understands why some politicians don't want to face up to the reality that Brexit has not delivered what they once promised.

'But it is time for a different conversation about what our long-term relationship should be.

'Sticking with the status quo and not working relentlessly to secure a good deal that boosts growth would be a major dereliction of duty.'

London Mayor Sadiq Khan stepped up his drive for rejoining the EU, saying the 'case has never been stronger'.

'The Mayor believes that walking away from our largest trading partner was the biggest act of economic self-harm in the history of our country,' a spokesman told the Standard. 

'That is why he wholeheartedly supports the Prime Minister's ambition to seek a closer relationship with the EU to put our capital, country and continent on course for a more secure and prosperous future.'

He added: 'The case for rejoining the EU has never been stronger – and Sadiq is clear that immediate steps should be taken to deepen integration with our European neighbours in order to boost our economy and drive-up living standards.'

More in Common polling released today underlined the scale of the challenge facing Mr Burnham in winning public support for any option.

Two-thirds of Brits were adamant a referendum would be needed to rejoin the EU.

But large proportions have tricky red lines, with 45 per cent saying any contributions to Brussels coffers would be unacceptable. Some 40 per cent insisted access to UK fishing waters would be a dealbreaker - even though EU boats have been granted rights even after Brexit.  

Tory frontbencher Andrew Bowie told Times Radio Mr Burnham's remarks on the referendum were 'dangerous and divisive'.

'We know that Russia and indeed Iran and other adversaries of ours around the world have been interfering or seeking to interfere in elections and referendums in this country and indeed within our allies for many, many years,' he said.

'But that Brexit referendum was a legitimate vote.

'People voted in this country in record numbers to leave the European Union. And I actually think it's very dangerous and divisive of the prime minister to reopen this debate in such an explosive fashion.

'He knows that the division that was sowed by that referendum, the best way to resolve any lingering issues around that referendum is to get on and make the most of what we have now through Brexit, the best of the trade deals that we have, and indeed the benefits that we can get from being outside the European Union, such as being exempt from Trump's tariffs that he introduced earlier this year.'