Losing both the Kingswood and Wellingborough by-elections means the Conservatives have established a new record – the largest number of defeats it has suffered in a single parliament.

A net loss of nine seats is one more than the eight defeats in the mid-1990s as John Major led the party to one of its heaviest general election defeats.

The odds of Rishi Sunak repeating that have increased.

The defeat in Wellingborough is one of the worst in the Conservative Party‘s long history. Peter Bone’s majority of more than 18,000 votes swept aside, with Labour winning with a 6,000 majority of its own. The Conservative vote fell by 38 percentage points, more than enough to erase its 36% majority.

By-election results live: Labour secures double victory

Wellingborough rewrites the record books. The decline in vote share from the preceding general election – 37.6 points – is the largest since 1945 and shatters the previous record 32-point fall in Christchurch in 1993.

Wellingborough becomes the eighth-largest Conservative majority overturned since 1945.

Six of the top 10 by-elections in that list are contests held during the current parliament.

There was a 28.5-point swing away from the Conservatives, not quite beating the record 29.1-point swing to Labour in Dudley West established in 1994, but easily the largest this parliament.

Labour was understandably quick to celebrate these numbers, using the Con to Lab swing to suggest that if this had been a general election the Conservative party would be all but wiped out.

An exaggeration, but Labour’s almost 20-point increase in vote share ranks among the best, marginally smaller than the improvement shown in the Rutherglen & Hamilton West, Tamworth and Selby & Ainsty by-elections earlier in this parliament.

The party has six by-election net gains this parliament, the most Labour has ever made.

A significant fraction of the collapse in Conservative vote share is explained by the 13% of voters who supported Reform.

How many of these were Conservative defectors is difficult to say, but there is no doubting the importance of this performance in the context of an imminent general election.

National polls suggest Reform has the support of one in 10 voters, about the same number intending to vote for the Liberal Democrats. Given that, polling 13% in a constituency where a clear majority voted to leave the EU in 2016, is about a par result but not an indication that the party can win seats.

However, Reform is a real threat, the catalyst for far greater Conservative seat losses than would otherwise be the case.

In Kingswood there was a small 21-point drop in the Conservative vote, but there too that was not mirrored by Labour’s increase of 12 points.

The difference is again explained by the 10% of voters who supported Reform. Here, as with Mid Bedfordshire and Tamworth beforehand, the combined votes of the Conservative and Reform exceeded those cast for the Labour winner.

The far smaller 16.4-point swing to Labour is in line with the swing suggested by current national polls, rather than repeating the scale of the Wellingborough victory.

This won’t worry Labour, of course, with a general election now less than a year away, a swing of this scale would give Sir Keir Starmer a Commons majority of 110 seats.

In both seats there was a sharp fall in turnout, falling by 26 points in Wellingborough but one of 34 points in Kingswood.

It would be wrong to say this came as a result of holding by-elections in winter weather because it reflects the indifference generally shown by electors throughout this parliament.

With the Rochdale by-election just two weeks away (the first by-election to be held on 29 February since 1944) it is prudent not to extrapolate too much from these two results. Labour has disowned its candidate there, although his name remains on the ballot paper.

If, as seems likely, Labour loses the seat, the Conservatives will exploit that to the full. Whether they succeed in halting Labour’s progress towards the next general election remains to be seen.