A number of tactical voting website have sprung up to help voters opt for the most pro-Remain candidate likely to win in a particular seat.
The First Past the Post system means your preferred party may stand very little chance of winning where you live.
The Liberal Democrats , Plaid Cymru and the Greens have already agreed to a Unite to Remain pact.
But the Lib Dems have come under fire for refusing to stand aside for pro-Remain Labour Party incumbents.
This came to a head earlier this week when the Lib Dem candidate in Canterbury Tim Walker pulled out to give Rosie Duffield a clear run.
Ms Duffield, who has rebelled against her party to oppose Brexit , was a surprise win for Labour in 2017 and holds the seat with just 187 votes.
But the Lib Dems have disciplined Tim Walker for pulling out and are insisting on standing a candidate.
They insist that they will not stand aside without Labour reciprocating and because they do not believe Jeremy Corbyn's party is really a remain-backing party despite the record of some of his MPs.
In some seats it will be very obvious who to back but for those who feel confused there are a number of websites offering guidance.
But there is disquiet among Remainers with concern that the three major tactical voting websites do not agree.
Remainunited.org (Gina Miller)
This website is backed by Gina Miller who has taken the government to court twice over Brexit - and won.
The format is very simple.
Users simply enter their postcode and are advised which of their local candidates they should back in order to return a Remain-backing MP.
Miller’s site will currently back about 50 Liberal Democrat candidates.
Remain United’s model suggests that the Lib Dems are likely to win only 33 seats if there is a significant tactical voting drive.
Her research suggests that the Tories are currently on course to win a majority, with 347 seats.
However with tactical voting she argues there could be a narrow majority for a coalition of Labour, Lib Dems and the SNP who could deliver a second referendum.
Her model – which uses polling that is then combined with demographic data and past voting to come up with recommendations – suggests tactical voting could reduce the Tories to 309 seats, with Labour on 233 and the Lib Dems on 33 seats.
She told the Observer: “If we don’t tactical vote, what we will end up with is a Tory majority that is going to pursue a Brexit plan that is no longer theoretical.
“It is not as though we don’t know what is going to happen. We know the direction of travel. If you look through the withdrawal agreement, it significantly shifts accountability. Executive power increases, while parliamentary scrutiny decreases.
"High-quality data is expensive and understanding it is time-consuming … inevitably, it upsets people in different parties
“What is going to upset a lot of parties is that we have no emotional attachment. This is going to be driven by the data and the results are quite different to the results out there already. I can foresee the Lib Dem seats going up [by] a handful, but it’s not going to be anything particularly dramatic.
“Our research is showing that between 45% and 55% are going to vote tactically. We’re starting from a different place to the 2017 election. But you can’t just go on past polling data or down party lines. We’ve used as many layers as possible.”
Getvoting.org (Best for Britain)
The pro-EU Best for Britain group published research showing the Conservatives would net a majority of 44 if no tactical voting took place.
But if 30% of electors “held their nose” and voted for a party other than their first choice they could derail the Prime Minister’s bid for a majority, the group insisted.
It published a website where voters can enter their postcode and be advised how to cast their ballot to give a Remain-supporting candidate the best chance of victory.
However, nearly a quarter of constituencies did not have data when the site launched and others threw up surprising results claiming a Lib Dem was best placed to win - even when recent past results suggested otherwise.
The tool is based on seat-by-seat analysis of 46,000 British people carried out by Best for Britain over September and October.
The analysis predicts the number of seats that will be won by each party under different tactical voting scenarios.
Under this scenario, a coalition of Labour, Lib Dems, SNP, Green and Plaid Cymru would hold a parliamentary majority of 4 seats.
If 40% of pro-Remain voters use their vote tactically, the coalition would return a majority of 36 seats.
But the people behind it warn that very same coalition could hold as few as 268 seats combined if voters are ineffectually split between them.
This scenario would see the Conservative Party win 364 seats and a majority in Parliament.
Best for Britain CEO Naomi Smith said: “99 per cent of polls this year have shown that the country is in favour of remaining in the European Union.
“However, through our first-past-the-post electoral system, we could still end up with a pro-Brexit majority in the House of Commons, elected on a minority of the vote share.
“We can’t change this system, but we can change how we vote, and we’ve found that four out of five voters are up for this.
"That’s why Best for Britain has commissioned the biggest tactical voting machine in the country and the results are clear. If we want to stop the disaster that is Brexit, we must vote tactically in the next general election .”
However Best for Britain faced a backlash after a number of their recommendations in specific seats were criticised.
People's Vote
The People's Vote has been beset by problems and splits recently but despite their internal issues.
They have launched a voting campaign investing their efforts in just 100 seats which they believe will decide the election.
They say they are focused on candidates rather than parties.
As such their recommendations are based on what the candidates themselves have said publicly and privately.
Their research uses private and public polling data.
It also uses information from election results at all levels going back several years.
It backs such disparate candidates as europhile Mary Creagh to long-term eurosceptic Dennis Skinner.
The Lib Dems are endorsed in both currently held seats and target seats - including those of switchers Chuka Umunna and Sarah Wollaston.
Plaid Cymru pick up two endorsements in Wales, though the Greens get none.
No Conservatives get the nod, while former attorney general Dominic Grieve is the only independent to be endorsed.
In Northern Ireland two Alliance Party, one SDLP and one UUP candidate are selected to try to break the hegemony of the pro-Brexit DUP and the abstentionist Sinn Féin.
Scotland, where the pro-Remain SNP holds the majority of seats, does not feature.
