Boris Johnson dumped dirt on May's Brexit deal in his bid to be viewed as a credible Plan B

Brexiteer rebel Boris Johnson travelled to JCB's headquarters in Staffordshire on Friday to dump some fresh dirt on Theresa May's Brexit deal.

The former foreign secretary, who quit her cabinet in protest over her Brexit blueprint plans last July, told an audience of factory workers that her deal with the EU was bad for Britain and that's why parliament had comprehensively voted her down.

He then went on to offer his boss some unsolicited advice about how to resolve the Brexit paralysis; Get back to Brussels and negotiate some more.

"If we hold our nerve, I believe we can deliver not a pseudo Brexit... but the Brexit people voted for," he said.

"It is time to go back fortified with the emphatic and conclusive mandate of parliament and demand real change to that backstop, and mean it this time so Britain can get out unilaterally and whatever they are saying I believe they will be flexible."

When I suggested to him he had come all the way to JCB's headquarters - at a moment of national crisis - to make his own leadership pitch in a bid to further undermine an already defenestrated prime minister, he insisted that he was only trying to "humbly and sincerely to offer a way forward".

But this was not a conciliatory speech. This was an audacious attempt to launch Mr Johnson as a credible Plan B as he sketched out the beginnings of an election manifesto, throwing out his thoughts on housing and hospitals, wages and taxation, crime and devolution.

He might have bottled a run at the leadership in 2016, but this former mayor of London is still hopeful that one day he might take the crown.

It is true that these days he is more a Marmite politician than a Heineken one. His starring role in the Brexit referendum campaign has left him loathed and loved in equal measure.

A couple of his colleagues have threatened to quit the Tories if he ever became leader, such is their dislike of this man.

And yet he remains top of Tory voters' and members' polls for who they'd like as the next Tory leader. Senior Brexiteers who also want a run at the job know he's the one to beat.

Mr Johnson admitted this week that he regretted pulling out of the leadership race in 2016.

"If I had my time again I might have done things differently," he said.

"I've certainly have engaged in a lot of heart searching about it ever since."

There's no doubt - despite his detractors saying he's a busted flush - that he still believes he could one day take the top job and he has built quite an operation around him in recent months to help him get there.

He is still close to Sir Lynton Crosby, the election strategist who ran Mr Johnson's two successful mayoral campaigns in 2008 and 2012 before going on to work for David Cameron in the 2015 election and Theresa May in 2017.

Sir Lynton's company CTF Partners tells me Mr Johnson has not hired them. But there is clear activity between CTF and the former London mayor: recent records show the MP received a £20,000 interest-free loan from the company as well as a £3,000 donation from the firm for "office and staffing costs".

Meanwhile, he has clearly got support from JCB founder and Tory donor Lord Bamford. He gave Mrs May £1m for her election war-chest; these days he's shutting down his shop floor to give Mr Johnson a stage - picking a winner some might say.

Of course, his rival Mrs May won a vote of confidence in her leadership in December and she cannot be challenged now for another 12 months.

But this Brexit paralysis may still bring her and her government down. And if it does, Mr Johnson is waiting.