Theresa May took to Facebook this weekend to declare that she – or more accurately, the Conservative Party that she leads – is a mere six parliamentary seats away from defeat in the election on 8 June, and if they lose that handful of MPs, Jeremy Corbyn will become the Prime Minister.

“The cold hard fact is that if I lose just six seats I will lose this election and Jeremy Corbyn will be sitting down to negotiate with the presidents, prime ministers and chancellors of Europe” Theresa May, 20 May 2017

You might be thinking that this is an incredible reversal of fortunes for the party that’s consistently held a double-digit lead in the polls since the election was called on 19 April. How can the Conservatives’ position be so shaky after weeks at the top?

Well, the answer is that it’s not quite that simple.

There are two big claims here from Mrs May. First, that the Tories would be kicked out of government if they lost just six seats. Second, that if they lost that handful of MPs, Jeremy Corbyn would walk into Downing Street on 9 June.

We’re not convinced by either.

Where is the “six seats” figure coming from?

We asked the Tories to show us their working, but they didn’t get back to us (we’ll update if they do). In the absence of an explanation from them, we’ve done our best to figure out how they’ve arrived at this number.

Start with the total number of seats the Conservatives won at the 2015 election (330). Then take the minimum number of seats a party needs to get a majority in the Commons (326). Now imagine that the Tories lose six of those 330. That would put the Conservatives on 324, two below the 326 they need.

We ran our calculations by Dr Nicholas Allen, Reader in Politics at Royal Holloway, University of London, to see if this would be a sensible way to work out Theresa May’s margin of defeat. He said “it’s not unreasonable for the prime minister to calculate what it would take to ‘lose’ the election based on the seats won in 2015. But [the six seats figure is] technically and politically wrong”.

He pointed out that if the Deputy Speakerships (which are excluded from the calculations of a government’s working majority) are distributed in the same way after the election as they are today (i.e., one Tory, two Labour), Theresa May “can lose 7 seats and still command a technical if narrow majority”.

But whether the figure stands at six or seven seats, it seems the Tories are promoting a pretty one-dimensional interpretation of the parliamentary arithmetic, and ignoring many of the factors that will ultimately decide this election.

We’ve taken a look at what’s changed in the polls in the last fortnight and how that might translate into seats in parliament – and ultimately, what it means for Mrs May’s and Mr Corbyn’s chances of being Prime Minister on 9 June.

What’s happening in the polls?

There’s been plenty of coverage this week charting Labour’s steady climb in the polls, with one putting the Tory lead over Labour at just nine percentage points. That’s the first time in this election that the figure has dipped below double-digits.

But before champagne corks start popping at Labour HQ, let’s remember that the so-called “poll of polls” conducted by Britain Elects, which takes an average of seven major measures of voting intention, still puts the Conservatives nearly 16 points ahead of Labour.

That’s not to say Labour can’t climb the mountain, but they should be under no illusions: they are still in the foothills.

What would this look like in parliament?

Thanks to Mrs May’s emphasis on individual leaders, it’s easy to forget that this election, like every other in British history, will still be decided by whichever party, or coalition of parties, commands a majority of the 650 parliamentary seats.

Our “first-past-the-post” voting system means that MPs are elected if they get the largest share of votes cast in their constituency. The effect of this is to skew national polling, which looks simply at what proportion of the total electorate intends to vote for one party or another. When we’re predicting which party will be in government, it’s all about distribution, distribution, distribution.

For example, in 1997, Tony Blair won a landslide of 419 parliamentary seats with only 43.2 per cent of the total votes cast nationally – giving Labour a 179-seat majority in the Commons. In that same election, the Conservatives received 30.7 per cent of the national vote, but were left with only 165 seats. The polls put them less than 12 points apart, but Labour landed 254 more seats than the Tories.

So in order to work out who will win this election, we need to consider voters’ views in each of the 650 parliamentary constituencies, not just nationally.

Here’s where the picture gets a little less rosy for Labour.

Electoral Calculus, which analyses opinion polls and “electoral geography” to help bridge the gap between polls and seats, puts the Conservatives on course for a 165-seat majority, and the chances of an overall majority for the Tories at 76 per cent, compared to 7 per cent for Labour.

What are the chances of Jeremy Corbyn becoming Prime Minister?

Mrs May’s statement suggests she wants you to think two things: 1) that the Tory lead is far from secure and 2) that Jeremy Corbyn has a real chance of becoming Prime Minister if she loses.

But if her “six seats from defeat” claim is to be believed, Labour would have to enter a coalition with every other party in parliament to give Jeremy Corbyn the 326 seats he’d need to govern. And that doesn’t look at all likely. The Lib Dems have ruled out a coalition with both Labour and the Conservatives, as have the SNP.

Electoral Calculus puts the probability of Jeremy Corbyn becoming Prime Minister on 9 June – either as head of a majority government or a Labour-led coalition – at just 11 per cent. The same data says Theresa May has an 85 per cent chance of remaining Prime Minister, if we include (albeit unlikely) Conservative-led coalition scenarios.

So is Theresa May just six seats away from defeat?

Yes and no. On a very basic interpretation of the current state of parliament, if the Tories’ share of seats falls from 330 to 324, they would no longer have a majority in the Commons (although even that ignores some of the intricacies of parliamentary arithmetic).

But more importantly, according to current polling, the chances of the Tories getting anything less than a landslide at this election are vanishingly small – let alone actually losing seats. And in the unlikely event that it did happen, it wouldn’t necessarily hand victory to Corbyn, as he’d need to convince every other party to enter coalition – which all sides have officially ruled out.

All the reliable data we’ve seen contradicts Mrs May’s suggestion that this election is on a knife edge.

Many are speculating on why she might want to give that impression. Her post majors heavily on what she apparently considers the calamitous prospect of Jeremy Corbyn becoming Prime Minister, “sitting down to negotiate with the presidents, prime ministers and chancellors of Europe”.

We asked Dr Allen for his take. He said: “May is probably trying to dampen down expectations of an enormous Tory landslide […] She needs to motivate activists. She needs to mobilise Tory voters, who might otherwise stay at home thinking it’s a dead cert. And she needs to manage her colleagues’ expectations. It’s always better to be seen to exceed expectations than under-perform”.

That may be the case, but it’s a gamble too, if it gives wavering Labour voters the impression that a Corbyn win is feasible. John Cleese’s party political broadcast for the Lib Dems in 1997 pointed out the tendency for people to avoid voting for a party if they think it’s got no chance of winning. If they think it’s in with a shot, enough voters could head to the polls to make victory possible.

Labour’s fortunes in this election have looked so bleak thus far that Theresa May might be worried that Tory voters will get complacent. Making a Corbyn premiership seem a realistic possibility could be one way to get out her vote.

Either way, we’re we’re not convinced that the election is anywhere near as close as she’d like you to think.