The Crewe by-election looks like it just might be a bit of a watershed for the Conservatives. It's the first time the Tories have won a by-election in a Labour-held seat since 1978 - 30 years ago. If David Cameron becomes PM, will everyone look back at this moment as the point where he really began to take control? Anyway, Crewe is miles away - why should London care?

Well, for one thing the infamous 1978 by-election was here in the capital. Ilford North to be precise. At the general election in 1974, Labour had squeezed home in Ilford, but by 1978 the Government was going through a tough patch - so this was always going to tricky for the young plucky Labour candidate...

...step forward: our very own Tessa Jowell. She may have lost, but only by a swing of 7% - and as we all know she came back to become our Minister for the Olympics.

So what happens next? Is the 10p tax rate for the Labour Government the equivalent of the Tories' early 90s 'drop out of the ERM' moment? They never regained credibility or popularity, and went through a series of disastrous by-election results before being trounced in 1997.

We shall see - and sooner than many may think. Mayor of London Boris Johnson MP is apparently just about to resign his Westminster seat, causing a by-election in his old constituency. (The fact he didn't resign til now shows a wise man covering his bases before this month's election, but hey...) Henley is of course a Tory stronghold - Boris took over 53% of the vote last time.

With a majority of 12,000 to over-turn, don't expect the Labour fight-back to begin on that election night...

Blurry Dave pic from Mick Y's Flickrstream