British Prime Minister Boris Johnson will begin a blitz of Labour's heartlands in a bid to convince Leave voters that Jeremy Corbyn's Brexit position is akin to a "great betrayal".

Mr Johnson will spend the three days before polls open targeting voters in traditional Labour strongholds, which his party views as key to securing a Conservative majority.

In a bid to help crack the so-called "red wall" of Labour seats across the North of England, the Conservative Party leader will spend today in the Leave-voting regions of the Humber and Wearside.

He will blast Mr Corbyn for sticking "two fingers up to the public" on Brexit during his tour of Labour seats.

Places like Grimsby have not been held by a Tory MPs since the Second World War.

In Sunderland - where Mr Johnson said Brexit's "roar" was heard for the first time on referendum night after the city's quick count showed a huge swing towards Leave - the PM will tell North East voters that it is Labour that has "let you down most of all" on Brexit.

"It's been the great betrayal, orchestrated from Islington by politicians who sneer at your values and ignore your votes," he will say.

It comes as the former Vote Leave figurehead's pledges on Brexit were brought into question after a second leak pored doubt on the country's ability to be ready to exit the European Union within a year.

Mr Johnson will tell voters on Wearside that there is only "three days to get Brexit done" - but a leaked government document suggests delivering customs arrangements related to Northern Ireland's post-Brexit relationship with Britain by December 2020 would be a "major challenge".

He has consistently vowed to take the UK out of the EU by 31 January and then finalise a trade deal with Brussels within 11 months to meet the transition period deadline.

Arrangements would also need to be signed off that allow Northern Ireland to continue to follow Brussels and Republic of Ireland rules on the trade of goods to ensure there is no hard border.

But a Whitehall report seen by the Financial Times highlights the difficultly involved for the British government in bringing in the infrastructure in time for the UK to leave when Mr Johnson has pledged.

A Department for Exiting the European Union document, according to the FT, states that: "Delivery of the required infrastructure, associated systems, and staffing to implement the requirements of the (Northern Ireland) protocol by December 2020 represents a major strategic, political and operational challenge."

Labour Party leader Jeremy Corbyn

Last week, Labour released a leaked Treasury report that concluded customs checks and possibly even tariffs could be required on goods travelling in both directions between Northern Ireland and Britain.

But Mr Johnson told Sky News' Sophy Ridge On Sunday programme that the report was "wrong" and added that the six counties would have "unfettered access" to the UK market.

Labour, in a further digging exercise through Mr Johnson's past writings, have unearthed further controversial comments made by the former London mayor.

Party officials had previously discovered an article from 1995 in which the ex-journalist was disparaging about single mothers and he has been criticised for describing Muslim women wearing burqas as looking like "letterboxes" in a column.

According to comments found by Labour in articles in the Daily Telegraph and Spectator magazine, Mr Johnson said it was "right" that Tories should wish its leadership to "speak up more strongly against...gays in the military".

He is also alleged to have complained that police were "deployed in desperate attempts to catch paedophiles in ancient public schools".

Meanwhile, Liberal Democrats leader Jo Swinson admitted it "doesn't look likely" her party will win a majority as she insisted the Lib Dems have led the campaign for a second EU referendum.

Asked about her party's manifesto pledge to revoke Article 50, Ms Swinson told BBC Radio 4's Today programme: "It's only in the circumstances of a Liberal Democrat majority government which of course in itself would be democratic.

"But where we are right now that obviously doesn't look likely."

"The most likely way we can stop Brexit is through a people's vote and the Liberal Democrats have led the campaign for a people's vote for three-and-a-half years," she added. 

Speaking on the same programme, DUP leader Arlene Foster accused Mr Johnson of breaking his word over protecting the union.

When asked about the sense of some in the unionist community that the Mr Johnson's deal was a "betrayal", Ms Foster said: "I think it is right for the leadership of unionism in Northern Ireland to try to work with the prime minister of the day to get the best deal for Northern Ireland.

"We will always do that. We will continue to do that. I think it says more about the person who broke their word than me and the leadership of the... Democratic Unionist Party."