Richmond By-Election: Lib Dems take an upset win, but all progressives must now keep their eyes forward, take the lessons and repeat the success elsewhere

For Tim Farron, the Richmond Park win is the perfect start to his second year in charge. Yet he and other progressives leaders must be aware how entangled are the fates of progressive parties. Photograph: Tim Farron at the Lib Dem conference rally on 19 September 2015 by Dave Radcliffe (License) (Cropped)

Last night the Liberal Democrats pulled off a pretty spectacular upset, overturning Zac Goldsmith's majority of 23,000 to oust him from his seat. Goldsmith, who though having stood down over Government plans to pursue Heathrow expansion nonetheless appeared to receive Conservative backing, was defeated in a second major election in a year.

But the win was not for the Liberal Democrats alone. Sarah Olney, the Lib Dem candidate and new Richmond Park MP, received support from the Green Party, some Labour MPs, the Women's Equality Party and other campaigners, all uniting around her as the progressive with the best chance to topple Zac Goldsmith - who had endorsements from both the Tories and UKIP.

That tentative venture into Progressive Alliance politics was soured a little by the hostile attitude of the official Labour position, but otherwise it proved a limited but important point: an alliance of progressive parties, behind a common candidate and on favourable ground, can defeat a Conservative candidate.

But perhaps the clearest lesson from Richmond Park, and perhaps it is right to include Witney as well, is that the Liberal Democrats pose a genuine threat to Tory seats - a lesson that should not be lost on Labour. Labour cannot topple the Tory majority alone: they need the Lib Dems to take seats away from them as well, in their head-to-head contests.

In the post-result speeches, defeated Labour candidate Christian Wolmar told Olney that Labour voters had lent their votes to her to defeat Goldsmith. But Labour need to keep in mind the reality that it is Labour who stand to gain most from Lib Dems taking seats from the Conservatives.

Especially if boundary changes come into force, Labour needs to take a pragmatic view of the challenge ahead. To defeat the Conservatives and get back into government, the shortest route will be to back whoever the ideal progressive candidate may be to challenge in each constituency.

While the by-election itself was pitched as a battle over Brexit, or over Heathrow, the reality is that the main impact will be on the Government majority. Theresa May was already governing with an extremely narrow majority, making it hard for her to ignore her own party's loud and organised far-right backbenchers.

As her majority is whittled away, the Prime Minister will have to chose between picking up votes from her backbenchers by pushing more starkly conservative positions, or finding opposition support for more moderate measures. And being caught between such forces, that limit her available moves, makes a fresh election look all the more desirable.

In a final note: Zac Goldsmith went from the favourite to be the next London Mayor, to being bounced out of Parliament in a by-election, in the span of just six months. If that sends no other message, hopefully it might serve as a reprimand for his horrid negative campaign to become Mayor.

A candidate who ran a divisive campaign for Mayor and had the backing of the forces of division, of cuts and Brexit, has been rejected in favour of one calling for openness and tolerance, with the backing of progressives of all stripes. In a tough year, that's a nice change.