Westminster is braced for a summer of scheming as Brexiteers and Remainers mass their forces for a looming election.
Pro-EU parties have vowed to step up cooperation after successfully uniting behind the Lib Dem candidate in Brecon.
There are claims the tactic could be used in scores of seats across England and Wales at a snap poll – which many expect within months as the government’s wafer-thin majority implodes.
But the pro-EU pact could also force Mr Johnson towards a tie-up with the Brexit Party.
Nigel Farage’s fledgling outfit scooped 10 per cent of the vote in the by-election yesterday – which combined with the Tories would have meant a comfortable victory.
Boris Johnson (left at No10 this week) has flatly rejected the idea of an electoral pact with Nigel Farage (right in London last month). But Tory MPs told MailOnline the PM will be forced to think again if there is a snap general election
There is a huge degree of uncertainty about the impact of an electoral pact. But an Ipsos MORI poll found this week that the combined vote share of the Tories and Brexit Party was 43 per cent. With Labour on 24 per cent and the Lib Dems on 20 per cent, the Electoral Calculus website suggests a Brexit alliance would have an enormous 268 majority in the Commons
In theory, the Tories would have comfortably won the Brecon by-election if they were in a pact with the Brexit Party
Mr Johnson has flatly rejected the idea of an electoral pact, but Tory MPs told MailOnline the PM was obliged to say that publicly, and would have to think again if there is a snap general election.
A formal alliance is considered unlikely, but there could be an understanding that the Brexit Party makes way in Tory target seats, and in return is given a clear run at constituencies in the North and Midlands where the Conservatives do not have a realistic chance of winning.
There is a huge degree of uncertainty about how a pact would function, and what kind of results it would produce at an election.
But as an indication, an Ipsos MORI poll found this week that the combined vote share of the Tories and Brexit Party was 43 per cent.
With Labour on 24 per cent and the Lib Dems on 20 per cent, the Electoral Calculus website suggests a Brexit alliance would have an enormous 268 majority in the House of Commons.
Mr Farage has claimed that US president Donald Trump would be fully in support of such a deal.
However, one obstacle is the presence in No10 of maverick Vote Leave chief Dominic Cummings.
The pair have a long-running feud from the 2016 referendum campaign, and Mr Farage has warned a deal is not possible while Mr Cummings is advising Mr Johnson.
The ‘Remainer Alliance’ between the Lib Dems, Greens, Plaid and independent MPs could focus on Tory seats that had large Remain votes in the 2016 referendum, and where the current majority is within reach.
Strategists estimate there is potential for large numbers of unashamedly anti-Brexit MPs to be elected by joining forces.
Analysis by political strategist James Kanagasooriam for Sky News’ Sophy Ridge on Sunday found a Remain Alliance could increase the number of explicitly anti-Brexit MPs in England and Wales from 27 to 66. The figure could rise to 154 if the new group performed particularly well in seats lower on its target list.
Lib Dem leader Jo Swinson this morning praised Plaid Cymru and the Greens for standing aside in Brecon & Radnorshire.
‘I do think that working across party lines is important when there is so much at stake for the future of our country and I will continue to do that,’ she said.
‘I’ve exchanged messages this morning with the Green and Plaid leaderships and I think there will be more co-operation in future elections.’
Ms Swinson pointed out that at the last election the Lib Dems did not field a candidate in Brighton Pavilions, which is held by the Greens’ only MP Caroline Lucas.
Anthony Slaughter, leader of the Greens in Wales, said the decision to stand aside in Brecon had been ‘vindicated’.
He said ideally there should be electoral reform, but added: ‘Until we elect a parliament in Westminster that will reform our system and bring our politics into the 21st century, we have to work within the system we have.’
Heidi Allen, a former Tory MP who now sits as an independent, said the Brecon result was ‘utterly brilliant’.
‘We are stronger when we work together and put country first,’ she said.
Ms Allen has said the Remainer alliance model should be used ‘in as many seats as we can’, suggesting it could ‘really make a difference’ in ‘between 100 and 200 seats’.
Analysis by political strategist James Kanagasooriam for Sky News’ Sophy Ridge on Sunday found a Remain Alliance between the Lib Dems, Greens, Plaid Cymru and independents could increase the number of explicitly anti-Brexit MPs in England and Wales from 27 to 66.
Naomi Smith, chief executive of the pro-EU Best for Britain campaign, said: ‘The success of Jane Dodds in Brecon and Radnorshire proves that when remain parties work together, they succeed.
‘While the Leave side has an inherent advantage in elections due to its vote being concentrated between only two parties whereas the pro-EU vote is split across at least four, working together can clearly help beat those odds.
Conservative chairman James Cleverly this morning pointed out the overall support for Brexit in Brecon was bigger than that for Remain – although he said that demonstrated why people should vote Tory rather than siding with Mr Farage.
Many believe an election is now looming with Mr Johnson’s working majority down to just one, and Tories threatening to defect to wipe it out altogether.
Allies of Mr Farage have warned that Mr Johnson must start ‘talking’ about an alliance – which he has so far flatly ruled out.
In simple terms an electoral pact means two or more parties working together at an election – far from a new idea.
However, large-scale pacts are incredibly rare in the UK mainly because political parties rarely agree on enough to strike an accord.
The last properly large scale electoral pact was 100 years ago. But agreements have been made between smaller parties at many recent elections.
For example, the Greens have previously agreed to make way for Liberal Democrat candidates in seats which are tight with the Tories.
There are two basic types of electoral pacts: Formal and informal – and both would likely need Boris to seek agreement from the Conservative Party chairman, board and Cabinet to proceed with either approach.
Striking a deal with Mr Farage without clearing it with his Tory colleagues would be too high risk and would be likely to spark a damaging mutiny.
An informal pact is much more likely than a formal one because it would enable both parties to maintain their independence and status as separate electoral vehicles.
An informal arrangement would be much easier to swallow for moderate Tories because it could be sold to them as a short term necessary evil to ensure the Conservative Party stays in power.
Both approaches would require Mr Johnson to have difficult conversations with local Conservative associations, either to tell candidates not to stand or to tell activists not to campaign against the Brexit Party.
A formal pact would effectively see the two parties working together and agreeing to a single slate of candidates.
It is not clear exactly how the two parties would arrive at an agreed list of candidates because such a move has not been attempted in decades.
The two parties would then campaign together to get those candidates elected.
Standing one Tory/Brexit Party candidate in each constituency would have obvious benefits.
Combining forces would, in theory, unite a major part of the electorate in each constituency behind just one pro-Brexit candidate.
However, a formal pact would also cause major headaches for Mr Johnson and Mr Farage.
For Mr Johnson it would likely mean alienating many of the moderate voters who backed the David Cameron-led Tories who will not want their vote to be associated with Mr Farage.
Many moderate Tory MPs would balk at the idea of sharing a platform with Mr Farage while many candidates would be left furious if they were asked to stand aside.
The Tory leader would also have to tear up his party’s age old commitment to fight in every seat across the UK.
That would be extremely unlikely to be well received by the Conservative rank and file and the unlucky Tory candidates ditched for Brexit Party picks.
However, any annoyance could be tempered by Mr Farage’s popularity with many Tory members.
A poll published in April found the former Ukip leader was the second most popular choice among Tory councillors to be the next Tory leader.
For Mr Farage it would mean hitching his anti-Establishment wagon to the party of the Establishment.
It would also mean going all-in on Mr Johnson being able to deliver the kind of divorce from the EU wanted by Brexit Party supporters.
Anything less than a ‘clean break’ from the bloc would cause serious damage to Mr Farage’s personal brand.
The other way forward would be for the parties to agree to an informal pact which would see them make way for each other in target seats.
For example, the Tories could stand aside or barely campaign in seats in northern England to give the Brexit Party a relatively clear run at Leave-voting Labour-held constituencies.
In return the Brexit Party could agree not to campaign in the Conservative Party’s southern heartlands and in the south west where the Tories will face a strong challenge from the resurgent Liberal Democrats.