Conservative MPs will never allow Boris Johnson to lead the party because of his attacks on Theresa May mean he is 'not a team player' who is destroying the party, his former Foreign Office deputy said.

Sir Alan Duncan said his former boss believes he can become 'Britain's Trump', but that his appeal is slipping with the British public.

The senior minister told The Times the Foreign Office had to 'invest an enormous amount of time handling' Mr Johnson during his period as foreign secretary.

Sir Alan urged Mr Johnson to abandon his ambition to lead the Tories, saying that he would not get enough nominations from colleagues in parliament and even if he did the Tory grassroots would not vote for someone so 'reckless'.

He said: 'He's an enormous character but not a team player, not intellectually focused. He's got a very untidy mind.

'And he doesn't know if he's a journalist or a politician, but he does know it's all about him.

Britain's junior Foreign Minister Sir Alan Duncan says former boss Boris Johnson was 'not a team player'

Sir Alan Duncan said Mr Johnson, pictured leaving his Oxfordshire home on Saturday, needs publicity because it 'is his cocaine. He needs a regular fix'

'The more he repeats what everyone can see is not credible, the more his own credibility disappears. His supposed solution is neither workable nor on offer.

'If he thinks he can go into the conference and undermine [Mrs May] I think he's kidding himself. I think the party will be for her and not for him.'

Sir Alan dismissed Mr Johnson's call for a Canada-style deal with the EU as 'doubling down into deeper nonsense'.

He also said said Mr Johnson needs publicity like a drug addict needs cocaine.

Sir Alan said that the ex-foreign secretary, who quit in July over the Chequers plan, 'needs a regular fix' of headlines and equates it with political power.

Sir Alan, who remains an FCO minister, told the Spectator that he was determined that the European Research Group (ERG) of hardline Eurosceptics would not turn the Tories into 'the mutant child of Ukip'.

Boris Johnson seen jogging near his Oxfordshire home. The former Home Secretary is due to attend Conservative Party Spring Coherence, which starts on Sunday

He told the magazine when he worked under Mr Johnson he tried to stay out of the news and be loyal to him and Mrs May.

He added: 'There was only room for one showman in the Foreign Office. I get on with the diplomacy.

'But for Boris? Publicity is his cocaine. He needs a regular fix.

'And he equates getting publicity with having political power and authority and respect.

'But I think what he doesn't realise is that whereas he used to be an electoral asset, that is now waning.'

In September, Sir Alan hit out at the former foreign secretary after his comments likening the Prime Minister to a suicide bomber, writing on Twitter: 'This marks one of the most disgusting moments in modern British politics.

'I'm sorry, but this is the political end of Boris Johnson. If it isn't now, I will make sure it is later.'

Asked about this by the Spectator, Sir Alan admitted it was a bit over the top, but added: 'We are at a very critical moment, where if we get this wrong, we have no Brexit, no government, Corbyn.

'We may even have a period of Parliament finding it very difficult to get any proper government together.

'So we are on the edge of very grave danger, and we've got to get it right, so my view is you've got to be 100 per cent behind Theresa May.

'Every step the ERG has taken to box her in has weakened our negotiating position and made international observers say: Where the hell is Britain going on this? Can they deliver? Is Brexit going to happen?

'You can only get a good deal if you've got a united party behind the Prime Minister doing the negotiating.

'My concern was that Boris was limbering up to have a go at her in Conference - and so, I thought, not acting in the national interest.'

Foreign Office minister Sir Alan described Mr Johnson's intervention as self-indulgent.

He added: 'He knows his so-called plan won't work – it is just unhelpful, destructive grandstanding.

'He is not acting in the national interest, just his own selfish interest. People won't stand for it any more. The Prime Minister needs full support, not more carping.

Boris Johnson may challenge her for Tory leadership after refusing to rule it out four times

'He thinks he can be Britain's Trump,' he said. 'It ain't gonna fly. He had enormous electoral appeal but sadly he's spent it. He risks bringing everything down.'

Former home secretary Amber Rudd said it was a fantasy to believe a Canada-style trade deal would ever be approved by parliament.

Downing Street also rounded on Boris Johnson last night following his latest attack on Theresa May's Chequers plan.

Insiders accused the former foreign secretary of putting jobs and national unity at risk.

In a 4,600-word article, he had claimed the Chequers proposals were a 'moral and intellectual humiliation' that would cheat the electorate.

And in a series of interviews, he refused four times to rule out challenging Mrs May for the Tory leadership.