What’s the balance of forces following the 2017 election, and what do the parties need to do to win power next time?

At the 2015 election, the Conservative position in parliament was of a small majority and just 37 per cent of the vote. However, in the far more important respect as far as British politics goes – seats, and vote share in those seats – David Cameron had created a hegemonic position for his party. There were precious few seats with small majorities and many seats the party had first gained in 2010 were in possession of majorities you’d expect to find in Tory fortresses. Even to become the largest party, Labour needed a swing of 5.4 per cent.

The position was so bleak that I likened the 2015 result to 1983 – an election which realistically wrote off the 1987 contest before it had started.

After Labour’s forward advance in 2017, the picture is very different: from astonishing Conservative strength to acute Tory fragility.

For the Conservatives, the number to fear is nine: that’s how many seats they would have to lose to be unable to do a deal with the Democratic Unionist Party, even if that party won every seat in Northern Ireland. (That is in of itself not going to happen, but we need not let that detain us at this point.)

The bad news is that a mere one-point swing from the Conservatives to Labour would see them lose 15 seats: Southampton Itchen, Pudsey, Hastings and Rye, Chipping Barnet, Thurrock, Preseli Pembrokeshire, Calder Valley, Norwich North, Broxtowe, Stoke-on-Trent South, Telford, Bolton West, Aberconwy, Northampton North and Hendon. In addition, a further 21 seats would fall to Labour if they can replicate their 2017 swing, which was in of itself only their fifth-best since 1945.

A 5.4 per cent swing now would mean a Labour majority of one, even assuming no gains in Scotland. The reality is that the SNP position is so fragile that even in the event that Labour were to gain no votes directly from the Scottish nationalists, a 5.4 per cent swing from Tory to Labour north of the border would add an extra 14 seats to the Labour tally – meaning that a 5.4 per cent swing would likely secure a Labour majority of 28.

To put the ease of Labour’s challenge into perspective: if they replicated any of the swings from Tory to Labour while they have been in opposition since 1964, they will be in office, albeit in some kind of ragbag coalition.

In order to not emerge as the governing party after the next election, Labour would have to be the worst-performing opposition since 1959 and to do worse than any party has done after losing three elections in a row ever. The contrast with the post-2015 picture, when Labour needed to equal its 1997 swing just to get a majority of one, speaks for itself.

As for the Liberal Democrats, their 2017 election result is rather like Labour’s 2015 one: it's a lot more dreadful than it looks at first glance. In fact, at first, the 2017 election looks like a great success: up from eight seats they won in 2015 to 12. Look a little longer, however, and the full horror of their position becomes clear.

There are just 39 seats in which the party is second. In better news, 28 of those are against the Conservatives and just seven are against Labour, while three are against the SNP and one is against Plaid Cymru. It always makes the Liberal Democrats’ life easier if it is clear which target they are better off attacking.

In addition, in only two of the seats where the Liberal Democrats are second to Labour are they less than 10,000 votes adrift: in Sheffield Hallam, where they trail by 2,125 votes, and Leeds North West, where they are 4,224 votes behind. But to make matters worse, both those seats were Liberal Democrat-held until 2017. A large chunk of the Liberal Democrat vote is reliant on the personal popularity of the sitting MP, and there is next to no chance that Nick Clegg will stand again in Sheffield Hallam, though there is some possibility that Greg Mulholland will re-fight Leeds North West.

The silver lining is, yes, that this means there is no tactical headache about whether to attack the Tories or Labour, but is comes with a hefty cloud.

The Conservative-Liberal battleground is more fertile than the Labour-Liberal one, but not a lot more. In 15 of the 28, they are second, but they have to close a gap of more than 10,000 votes to take the seat. In just five of the seats do they need to close a gap of less than 5,000 votes, traditionally the level at which a seat is considered winnable by a rival party. In Montgomeryshire, which the party held at every election from 1906 to 2010 with the exception of 1979, they are 9,285 votes behind – closer to Labour in third place than they are to the Tories in first.

Realistically there are ten seats, five currently held by the Conservatives, two apiece by Labour and the SNP, and one by Plaid Cymru, that the Liberal Democrats can realistically hope to gain at the next election.

Gaining ten seats would be a great night for the Liberal Democrats by anyone’s standards, but the worse news is that once you go beyond that ten, the picture is bleak in the remaining 29 seats where they are second, and even worse elsewhere. They have fallen away even in areas of Liberal Democrat strength. Watford is probably the most dispiriting example for the party: they hold the mayoralty and the majority of seats on the council, but are an astonishingly poor third, a little under 20,000 votes behind second-placed Labour, and 22,000 votes behind the triumphant Conservatives.

In Inverness and Brent Central, both Liberal Democrat-held until 2015, they are fourth. In Southport, which they held until 2017, they are third, almost 3,000 votes behind Labour in second and close to 6,000 votes behind the Conservatives. And these are representative, rather than particularly awful snapshots of the Liberal Democrat position in the country.

Another party who have a worse electoral map than the headline result might suggest are the SNP. They not only lost seats but have gone from being a party of super-majorities to one that has just four seats – Kilmarnock and Loudoun, Dundee West, Dundee East, Ross Skye and Lochaber – with majorities over 5,000, and none with a majority over 7,000.

More troubling for them is that the pattern in both the 2016 Scottish elections and the 2017 general election was of increasingly effective tactical voting to defeat the SNP. It wasn’t clear in a lot of seats which the best way to kick the SNP was – it will be much easier for anti-nationalist voters to make that calculation next time. In addition, even if they hold on to their votes, they are intensely vulnerable if there is any kind of Conservative to Labour swing or vice versa.

And here, it is once again, Labour, who are the best-placed to benefit.

That’s the major story of the battleground in 2022: one in which the Liberal Democrats have a great deal of work to do, and the Conservatives and SNP are both highly vulnerable given they will be 12 and 15 years in office at the time of the next election. Meanwhile, Labour face an electoral map that makes them, on paper at least, the heavy favourites next time.