If tactical voting catches on in England, Boris Johnson has something to worry about - Brian Wilson

It’s a while since we’ve had a Liberal revival story so the Chesham and Amersham result is quite nostalgic.

Liberal Democrat leader Ed Davey and new Liberal Democrat MP for Chesham and Amersham, Sarah Green, during a victory rally at Chesham Youth Centre, Chesham

Turning a Tory majority of 16,000 into a Lib Dem one of 8000 is spectacular by any standard.

By all accounts there were significant local factors at play including hostility to HS2 – which the Lib Dems support nationally but opposed locally. Plus ça change!

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Perhaps the most interesting straw in the wind was the scale of tactical voting, which the outcome depended upon. The Labour vote virtually disappeared and was certainly the difference between glory and frustration for the Lib Dems.

That will concern the Tory high command more than the actual result. Tactical voting has never really caught on in England to the same extent as Scotland where it was deployed first in the 1980s to defeat Tories and, more recently, to prevent SNP majorities. Voters are wise to its potential.

In theory, tactical voting between Lib Dems and Labour supporters should not be too difficult if a point is reached at which there is a prevailing mood to get rid of Boris Johnson’s government. That possibility will be much spoken of and written about in the days ahead.

What Scotland teaches, however, is that “top-down” attempts to organise tactical voting are unlikely to succeed. There has to be that consensus among voters themselves which persuades them to do something they have not previously contemplated.

A high level Lib-Lab pact remains unlikely but an unspoken understanding on the ground carries far greater potential threat.