Help! My lock's seized up and my bike is trapped!

I very much doubt that a lock you recently used is now 'siezed' it could've been a bit stiff which wouldve totally been solved by the GT85. I think its likely to be some sort of mechanical jam.

Id recommend a lot of jiggling about/shaking it/hitting it.

Also bear in mind that someone may have glued your lock which is surprisingly common.

Hmmm, I hadn't thought about anyone gluing it, but that's a possibility. It came on very suddenly, yesterday afternoon, after the bike was locked up unattended in EC3 for about ten minutes. I managed to get it undone, locked the lock round my waist, and later had to be GT85ed free by a gallant chap in a bike shop. I really shouldn't have been stupid enough to lock it up again - this is my own fault. And this has happened before, with the same model of lock (10th February - I just searched my old posts), also on a rainy day - so I am more inclined to blame the weather. Hopefully I can just go back to Condor and wangle a replacement, like I did before, but to do that I have to get the bloody thing off in the first place...

And yes, I've been jiggling it, shaking it, hitting it, bashing it against things, cuddling it, poking it, wrenching it, coaxing it, swearing at it, praying to it - you name it.