Mr Farage announced the Brexit Party would not fight any seat that the Tories won in 2017 to boost the chances of Mr Johnson securing a majority on 12 December and taking the UK out of the EU.
Having previously insisted the Prime Minister’s deal with Brussels was “not Brexit”, Mr Farage said his “unilateral” electoral pact ruled out the prospect of second referendum on EU membership.
Sturgeon says Tory voters should be 'appalled'
First Minister Nicola Sturgeon said Conservative voters would be “appalled to find that their party has effectively become the Brexit Party”.
And the Scottish Liberal Democrat campaign chair Alex Cole-Hamilton MSP said the Tories had effectively been “endorsed by both Trump and Farage”.
The announcement does not guarantee Mr Johnson a majority, particularly if the Brexit Party presses ahead with plans to field candidates in Labour-held seats.
Brexit candidates could prove decisive
With polling showing the Tories set to lose two voters for every Labour voter switching to back Mr Farage’s party, Brexit candidates could still prove decisive in preventing a Tory breakthrough in vital battlegrounds across the north of England.
But the U-turn does protect the Tories from anticipated losses in south-west England, where the Lib Dems threaten to make gains, and in Scotland, where a number of Tories are defending small majorities against the SNP. One Scottish Tory candidate defending their seat welcomed the news, telling The Scotsman it would be “helpful”.
'Disappointment' inside the Brexit Party
Les Durance, the Brexit Party’s candidate in Moray, said: “I am disappointed with the announcement, I put a lot of work in over in Moray, which voted by nearly 50 per cent to Leave the European Union in 2016.
“I do understand Nigel’s rationale though, he has put country before party. In Moray I suppose the prognosis was that we would have split the vote and possibly allowed the SNP to take the seat.
“It is an enormous concession and I just hope that Boris honours his commitments.”
Mr Durance will now contest Inverness, Nairn, Badenoch and Strathspey, which is held by the SNP.
The Brexit Party leader said he had taken the “difficult decision” not to contest the 317 seats held by the Tories at the last election amid fears it could lead to a hung parliament and a second referendum.
The announcement was welcomed by the Prime Minister who said it was recognition that only the Conservatives could “get Brexit done”.
Threat to stand 600 candidates falls flat
Mr Farage had previously threatened to stand candidates in some 600 seats unless Mr Johnson abandoned his withdrawal deal with the EU.
But after the Conservatives rejected his offer of a “Leave alliance” he came under intense pressure from within his own party not to risk splitting the pro-Brexit vote.
His long-time ally - millionaire backer Arron Banks - announced plans for a tactical voting app which would have urged voters in hundreds of constituencies to support the Tories.
Addressing a Brexit Party rally in Hartlepool, Mr Farage said he had decided to pull back amid concerns his party could have let in significant numbers of Liberal Democrats.
“I think this announcement today prevents a second referendum from happening,” he said.
“And that to me, I think right now, is the single most important thing in our country.
“So in a sense we now have a Leave alliance, it’s just that we’ve done it unilaterally.
“We’ve decided ourselves that we absolutely have to put country before party and take the fight to Labour.”
'It's still not the Brexit we voted for'
Mr Farage said he still believed the Withdrawal Agreement negotiated with Brussels would not deliver “the Brexit we voted for” in the 2016 referendum.
However, he said he had been encouraged by statements from Mr Johnson at the weekend saying he would not extend the planned transition period beyond the end of 2020 and that he would seek a “super-Canada-plus” style free trade agreement with the EU.
“We are going to keep saying: remember you told us we were leaving at the end of 2020,” Mr Farage added.
“Remember you told us we’re not going to have political alignment. He will know, just as Mrs May’s vote disappeared in the European elections of this year, the same will happen again if a British prime minister breaks firm commitments and promises made to the British people.”
Farage claims he was offered peerage
The former Ukip leader claimed that he had been offered a peerage by the government, but insisted that was not a factor in his decision to stand aside in favour of the Conservatives.
“I was offered one last Friday,” Mr Farage said. “Ridiculous – the thought they can buy me, a high-paid job; but I’m not interested, I don’t want to know.”
Chris Curtis, head of political research at pollsters YouGov, said: “It is still the case that most marginal seats are Labour-Conservative battles and this is the most important dynamic in deciding who will be celebrating Christmas in 10 Downing Street.
“Given this, Farage’s decision to stand aside in current Conservative-held seats and not in Labour-held seats that the Tories will be looking to gain will likely make very little difference.”
'I didn't call Farage about a deal': Johnson
Nevertheless, the move was still welcomed by Mr Johnson, who flatly denied that he had called Mr Farage to agree a deal.
“I’m glad that there’s a recognition that there’s only one way to get Brexit done and that’s to vote for the Conservatives,” he told reporters on the campaign trail in Wolverhampton.
In a statement posted on twitter, the Prime Minister added: “If we have another hung Parliament it would lead to two more chaotic referendums next year.
“The Conservatives only need nine more seats to win a majority and leave by the end of January with a deal.
“We can then finally move on as a country, and focus on the priorities that matter to you and your family.”
The First Minister said the announcement “proves beyond any doubt that Boris Johnson and Nigel Farage are joined at the hip”.
“Any form of Brexit that is acceptable to Nigel Farage is going to be deeply damaging to Scotland, and I suspect there are going to be many traditional Tory voters in Scotland and across the UK that are going to be appalled to find that their party has effectively become the Brexit Party,” Ms Sturgeon said.
“If you vote Tory, you get the Brexit Party and it’s view of the world. That’s not what Scotland needs. I don’t believe that’s what the vast majority of people in Scotland want.
“But it does underline the view that if we don’t take our future into our own hands, that future is going to be dictated by Nigel Farage, Boris Johnson and increasingly extreme, right-wing Conservative Party.”
Jeremy Corbyn's response
Labour leader Jeremy Corbyn said Mr Farage’s move could pave the way to a US trade deal, giving American pharmaceutical companies access to the NHS.
“One week ago Donald Trump told Nigel Farage to make a pact with Boris Johnson. Today, Trump got his wish. This Trump alliance is Thatcherism on steroids,” he said.
Mr Cole-Hamilton called on moderate Conservatives to back the Lib Dems, adding that “Ruth Davidson’s attempts to detoxify the Scottish Conservatives are now utterly dead in the face of this unholy alliance.”