Imagine you are worried about a destructive Brexit. One that would damage the economy, undermine our influence in the world and possibly tear the country itself apart. And you think such an outcome is more likely if Theresa May emerges on 9 June with untrammelled power.

The Prime Minister is bad at consulting at the best of times, as we’ve seen with her dementia tax. Think what she’d be like if she wins the election with a three-digit majority.

How should you vote?

Easy, you might say. Labour.

Not so fast. For a start, Jeremy Corbyn’s policy on Brexit hasn’t been great. He has failed to provide any real opposition to the Tories. He has decided to quit the single market, meaning he too would damage the economy. And he won’t let the people vote on whether they still want to quit the EU when they finally know what Brexit means.

UK General Election 2017 Show all 47 1 /47 UK General Election 2017 UK General Election 2017 12 June 2017 British Prime Minister Theresa May leaves 10 Downing Street for the 1922 committee on June 12, 2017 in London, England. British Prime Minister Theresa May held her first cabinet meeting with her re-shuffled team today Getty Images UK General Election 2017 12 June 2017 DUP leader Arlene Foster stands alongside deputy leader Nigel Dodds as they hold a press conference at Stormont Castle as the Stormont assembly power sharing negotiations reconvene following the general election on June 12, 2017 in Belfast, Northern Ireland. Discussions between the DUP and the Conservative party are also continuing in the wake of the UK general election as Prime Minister Theresa May looks to form a government with the help of the Democratic Unionist parties ten Westminster seats. 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Getty Images UK General Election 2017 12 June 2017 British Prime Minister Theresa May (C, L) holds the first Cabinet meeting of her new team. Getty UK General Election 2017 11 June 2017 British Prime Minister Theresa May attends church in her constituency with her husband Philip May, a few days after disappointing results in a general election. Rex Features UK General Election 2017 9 June 2017 Leader of the Labour Party Jeremy Corbyn leaves Labour Party HQ this morning, following a general election yesterday. Parliament is hung, with no individual party gaining an overall majority. Post general election reaction. Rex UK General Election 2017 9 June 2017 BELFAST, NORTHERN IRELAND - JUNE 09: DUP leader and Northern Ireland former First Minister Arlene Foster (C) holds a brief press conference with the DUP's newly elected Westminster candidates who stood in the general election Getty Images UK General Election 2017 9 June 2017 A " Get May Out" demo took place opposite the gates of Downing Street, calling for May to resign, after the shock election results and Mays coalition with the DUP. Rex Features UK General Election 2017 9 June 2017 A demonstrator wears a mask depicting Britain's Prime Minister and leader of the Conservative Party Theresa May, poses with a mock gravestone bearing the words "Hard Brexit, RIP", during a protest photocall near the entrance 10 Downing Street in central London AFP/Getty Images UK General Election 2017 9 June 2017 Britain's Prime Minister Theresa May arrives at the Conservative Party's headquarters in London Reuters UK General Election 2017 9 June 2017 Britain's Prime Minister and leader of the Conservative Party Theresa May flanked by her husband Philip delivers a statement outside 10 Downing Street in central Londo Getty UK General Election 2017 9 June 2017 Britain's Prime Minister and leader of the Conservative Party Theresa May leaves Buckingham Palace in London the day after a general election in which the Conservatives lost their majority Getty Images UK General Election 2017 9 June 2017 A TV cameraman watches the door of 10 Downing Street in London Getty Images UK General Election 2017 9 June 2017 Labour leader Jeremy Corbyn is greeted by his Office Director Karie Murphy as he arrives at Labour Party HQ in Westminster, London, after he called on the Prime Minister to resign, saying she should 'go and make way for a government that is truly representative of this country' Dominic Lipinski/PA Wire UK General Election 2017 9 June 2017 Britain's Prime Minister Theresa May arrives at the Conservative Party's headquarters with her husband Philip in London REUTERS/Peter Nicholls UK General Election 2017 9 June 2017 Ukip leader Paul Nuttall speaks during a press conference at Boston West Golf Club where he announced that he is standing down as party leader Joe Giddens/PA UK General Election 2017 9 June 2017 Ruth Davidson, leader of the Scottish Conservatives, leaves the counting centre for Britain's general election with her partner Jen Wilson in Edinburgh, Scotland REUTERS/Russell Cheyne UK General Election 2017 9 June 2017 Scottish Labour leader Kezia Dugdale celebrates with candidate for Edinburgh South Ian Murray as he retains his seat at the Meadowbank Sports Centre counting centre in Edinburgh, Scotland Getty Images UK General Election 2017 9 June 2017 First Minister Nicola Sturgeon speaks to the media at the Emirates Arena in Glasgow, as counting is under way for the General Election Andrew Milligan/PA Wire UK General Election 2017 9 June 2017 Scottish Conservative leader Ruth Davidson at Meadowbank Sports Centre in Edinburgh, as counting is under way for the General Election PA UK General Election 2017 9 June 2017 Scottish National Party (SNP) leader Nicola Sturgeon reacts at the Emirates Arena in Glasgow, Scotland EPA UK General Election 2017 9 June 2017 Jeremy Corbyn, leader of Britain's opposition Labour Party, arrives at the Labour Party's Headquarters in London REUTERS/Marko Djurica UK General Election 2017 9 June 2017 UKIP Leader Paul Nuttall leaves in a car following the vote count for the constituency of Boston and Skegness in Boston, England Anthony Devlin/Getty Images UK General Election 2017 9 June 2017 British Prime Minister and Conservative Party leader Theresa May speaks at the declaration at the election count at the Magnet Leisure Centre in Maidenhead, England. Getty Images UK General Election 2017 8 June 2017 A policer officer enters a polling station in London AP UK General Election 2017 8 June 2017 A woman leaves after casting her vote at the Hove Museum and Art Gallery near Brighton, in southern England Getty UK General Election 2017 8 June 2017 A polling station sign is seen on a telephone box outside the polling station at Rotherwick Hall, west of London Getty UK General Election 2017 7 June 2017 A woman walks past a general election display in the window of a betting shop in Camden on June 7, 2017 in London, United Kingdom. Britain goes to the polls tomorrow, Getty Images UK General Election 2017 7 June 2017 Britain's Prime Minister Theresa May visits Atherley Bowling Club during an election campaign visit on June 7, 2017 in Southampton, England. Britain goes to the polls tomorrow June 8 to vote in a general election. Getty Images UK General Election 2017 6 June 2017 A supporter wears a pair of Jeremy Corbyn decorated tights at a general election campaign event in Birmingham, central England, on June 6, 2017. Britain goes to the polls on June 8 to vote in a general election only days after another deadly terror attack in the nation's captial. AFP/Getty Images UK General Election 2017 6 June 2017 A picture taken in London, shows election leaflets from various parties displayed ahead of the United Kingdom's general elections. Britain goes to the polls on June 8 to vote in a general election only days after another terrorist attack on the nation's capital AFP/Getty Images UK General Election 2017 6 June 2017 Election workers, George Gaunt and Luca Tragid deliver the first ballot boxes, on the Royal Mile in Edinburgh AFP UK General Election 2017 6 June 2017 British Prime Minister Theresa May meets with Conservative party supporters during an election campaign visit to a bakery during an election campaign visit on June 6, 2017 in Fleetwood, north-west England. 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If elected in next week's general election Mr Corbyn is pledging to create a million new jobs and to scrap zero-hours contracts Getty Images UK General Election 2017 1 June 2017 Scottish Conservative and Unionist Party leader Ruth Davidson joins a selection of Scottish Conservative election candidates and activists during campaigning on May 1, 2017 in South Queensferry, Scotland. With only seven days to go until the general election on June 8th, polls are showing the SNP out in front and the Conservatives set to close in on Labour. Getty Images UK General Election 2017 29 May 2017 Prime Minister Theresa May canvasses in Richmond with Conservative candidate Zac Goldsmith on May 29, 2017 in London, United Kingdom. After suffering defeat in the London Mayoral election Zac Goldsmith resigned over the Government's position on Heathrow expansion. He stood as an Independent but lost in a by-election to the Liberal Democrats. Britain goes to the polls on June 8 to elect a new parliament in a general election Getty Images UK General Election 2017 22 May 2017 Liberal Democrat leader Tim Farron poses for a selfie taken by carer April Preston during a General Election campaign visit to the Barlow Medical Centre, in Didsbury, Manchester Yui Mok/PA UK General Election 2017 22 May 2017 Britain's Prime Minister Theresa May speaks at an election campaign event in Wrexham, Wales Reuters UK General Election 2017 22 May 2017 Britain's main opposition Labour Party leader Jeremy Corbyn, and Labour's former deputy Prime Minister, John Prescott, exit the party's general election campaign 'battle' bus as they arrive at an event in Kingston upon Hull, northern England Getty Images UK General Election 2017 22 May 2017 Britain's main opposition Labour Party leader Jeremy Corbyn walks with supporters between venues, before speaking again at another general election campaign event in Kingston upon Hull, northern England Getty Images UK General Election 2017 22 May 2017 An anti-fox hunting protester is taken away and arrested by police outside the venue where Britain's Prime Minister Theresa May was due to launch the Welsh Conservative general election manifesto at Gresford Memorial Hall in the village of Gresford, near Wrexham, North Wales, on May 22, 2017. 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Sure, Corbyn says he won’t crash out with no deal – something May and her cabinet ministers threaten every other day. So Labour’s policy is definitely better than the Conservatives’. But there’s another factor to take account of: Labour is going to struggle to hang onto the seats it has got, let alone win any more.

What about the Liberal Democrats or the Greens, then? They have good Brexit policies. They want Britain to stay in the single market. They are also promising the people a referendum on the final deal. So where either party has a chance of winning, it makes sense to back them. The snag is that, even if one is being optimistic, there are only a few dozen seats where that’s the case.

Vote tactically then. Simply back the candidate which has the best chance of beating the Tories wherever you live. Isn’t that the solution?

Well, yes and no. If there’s a chance of kicking out a Tory Brexiteer, go for it. But there are three problems with this simple rule.

First, some Conservative candidates have been prepared to stick their neck out and oppose Theresa May’s Brexit policies. Not many, it must be admitted. Most of those who campaigned for Remain during the referendum are now toeing the party line.

But some, such as Nick Herbert, defied May’s whips and abstained in the Article 50 vote. Kenneth Clarke even voted against triggering Article 50. Others, such as Nicky Morgan and Anna Soubry, fought for Parliament to get a meaningful vote on the final Brexit deal – again flouting the Prime Minister’s will.

General Election Round-up: May 22

It makes sense to back these Conservatives. In a Tory-dominated House of Commons, one of the few brakes on a destructive Brexit will be people within the Prime Minister’s own party who are prepared to challenge her.

Another problem with the simple anti-Tory tactical voting rule is that there are vast swathes of the country where there’s no chance of removing them. In most of these seats, Labour is second. But tactical voting is pointless because it won’t change anything.

A better approach in these constituencies is to vote for one of the genuinely pro-European parties - the Greens or Lib Dems. That, of course, won’t change who is the MP either. But at least it will boost these parties’ share of the national vote, giving them a stronger platform from which to oppose a destructive Brexit. In these seats, a vote for Corbyn’s Labour is a wasted one.

The final problem with the simple anti-Tory voting rule is that it doesn’t say what you should do if Labour is defending a seat. Easy, you might say, back them.

But, again, not so fast. For a start, there are nine Labour Brexiteers, standing for re-election. Almost all are in safe seats. But even so, it is surely better to register a protest vote by supporting a genuinely pro-European party. And in Vauxhall, where Kate Hoey is facing a stiff challenge from a Lib Dem, those opposed to a destructive Brexit should rally around him.

What’s more, there are quite a few safe Labour seats where the candidate voted Remain during the referendum but is now going along with Corbyn’s spineless Europe policy. Going meekly into the polling booth and putting one’s cross against their names won’t do anything to stop a destructive Brexit.

The better approach, again, is to back the Greens or Lib Dems. They won’t have a chance of winning. But voting for them won’t put these safe Labour candidates at risk either. What it will do is boost the national share of the genuinely pro-European parties – and that is worthwhile.

Of course, voters should always support Labour MPs who continued to fight a destructive Brexit since the referendum – say by rebelling against Corbyn’s edict that they should vote in favour of triggering Article 50. And they should ride to the rescue of any Labour MPs who are under threat from the Tories. But otherwise, people should vote for a party they really believe in.

So what is one left with? A fairly complex situation, with the best party to back depending on the parties’ positions, the candidates’ views and the seat’s win-ability.

InFacts, the journalistic website I edit, has produced an interactive guide that applies these principles to all the constituencies in England and Wales. It’s not a black box as in each case we give reasons for our recommendations.

Those looking for a magic formula to wish away last year’s referendum result won’t find what they are looking for. But it will appeal to those who want to stop a destructive Brexit and are determined to make their votes count. This might involve voting for a party you have never imagined voting for previously. It would be worth it.