Why has the Tory majority of 16,000 votes been overturned?
It’s a by-election upset that virtually no-one expected, certainly not the Tories.
Voters in Chesham and Amersham abandoned the Conservatives in what had been a stronghold for the party for nearly half a century.
Instead the Lib Dems triumphed and their candidate Sarah Green was elected with a majority of more than 8,000.
Local issues were important - hostility to the HS2 rail link was a big factor - as well as concerns about planning reform that many fear takes power out of the hands of local people.
Watch Ed Davey celebrate the victory by destroying a blue wall, representing Southern Tory seats:
But there’s no doubt, the result has wider implications.
Voters we spoke to said money seemed to be going to the North of England, at the expense of the South.
They accused the government of complacency and ignoring them.
Boris Johnson’s personality, which played so well in places such as Hartlepool, also seems to go down less well here.
When I asked one voter why people had turned away from the Conservatives, she replied simply "well, do we trust Boris?"
Libby asks voters why this traditional Conservative seat was won by the Lib Dems:
It may be an overstatement to say the Blue Wall in the South of England is crumbling but some Tory MPs will be feeling nervous today - with good reason.
Labour MPs too will be asking whether Sir Keir Starmer could be doing more to rebuild the party’s fortunes after a dismal result last night.
Both opposition parties could soon face a dilemma over whether some kind of electoral pact may now be the only way to oust the Tories at the next General Election.
For more from our political team, listen to Calling Peston: