Press on the bus are not being allowed out but journalists who were not invited on have been able to film and interview the protesters.

Police attended the scene as three protesters remained in front of the bus.

They appear to have stuck themselves to the vehicle. Johnson is not on board.

Extinction Rebellion protesters, some dressed as bees, gathered around the Conservative campaign bus as it tried to leave JCB in Uttoxeter.

Climate protestors have glued themselves to Boris Johnson’s election battle bus as they said a key Tory pledge on the environment was a “death sentence for everybody”.

One activist, who identified himself as James, said: “We’re from Extinction Rebellion.

“The Conservatives have failed for the duration of the entire general election campaign, with only two days to go, to raise the prospect of the climate and ecological crisis which is facing humanity and all life on this planet.

“It’s going to severely impact our society and generations of British people to come and people around the planet.

“The Conservatives have a decarbonisation target of 2050, which is quite frankly a death sentence for everybody.”

‘Polls can be wrong’

Earlier, Johnson insisted polls which put him on course for a big victory in the election could be “wrong” as he attempts to persuade Tory voters to turn out on Thursday.

The prime minister warned Leave voters that the prospects for Brexit would be “appalling” if voters return another hung parliament in Thursday’s election.

The Tories have sought to unite Leavers, including ex-Labour voters, behind the party but fear they could stay at home rather than back Johnson.

Labour has promised to keep the option of leaving the EU alive by giving voters a choice between Brexit with a deal negotiated by Jeremy Corbyn or remaining in the EU.

But Johnson told workers at the JCB plant in Staffordshire: “I don’t see any alternative but a working majority to deliver it.”

The PM, who earlier bulldozed his way through a symbolic wall daubed with the word “gridlock” at the firm which donated tens of thousands of pounds to his leadership campaign, also denied that the Tories were now “home and dry” in the election.

“Absolutely not,” he said. “This is a very close fought election and we need every vote, the only mathematical alternative to a working majority Conservative government is the real, real risk of another hung parliament - that’s another five years of dither, delay and division, we cannot go down that right.

“I’m sorry to say this but remember what happened in 2017 - polls can be wrong and we need to be fighting for every vote.”

Johnson declined an invitation to say he would leave the country if Jeremy Corbyn is prime minister.

But as one worker joked that anti-Brexit MPs would be “sacked” on Thursday, the PM appeared to betray some last minute nerves about the Labour challenge in his own seat, which is not exactly safe.

“I’m hoping to keep my own seat,” he said.

Johnson meanwhile suggested he would eventually give the go-ahead to the HS2 high speed rail project, despite ordering a review which has put its future in doubt.

The PM said he is “temperamentally very much inclined” to go ahead with HS2 if Douglas Oakervee, who is leading the review, recommends it.

Asked if he would go ahead with the rail scheme, Johnson said: “HS2 I think is a scheme that is running now at £88bn in estimated costs, projected costs, I think it could go higher to be perfectly honest.”

He added: “If there is a chance to make HS2 work better, or if he (Oakervee) says it’s a bad idea then obviously we will have to look very seriously at that. But I want to give you my instincts. I think I’m probably the candidate at this election who has done the most to build massive infrastructure projects, I know a bit about it.

“I’m a massive enthusiast for it. On the whole, this country is woefully under-provided for fantastic infrastructure. So whatever Doug says, whatever his team says, I’m going to be temperamentally very much inclined to want to go ahead with a great national project if I can.

“But I’m also going to want to be able to save whatever money I can, those are going to be the instincts I will use when approaching it.”