Finally got round to visiting the police. A very helpful bunch, though possibly a bit clueless here and there. Then they did claim that they had not been around when my lock was replaced (apparently officially police has to be there, when you're not around personally). "Did you talk to your landlord yet, sir? He's allowed to make improvements to your place without your consent". Fortunately they didn't give the obvious reply when I asked:"How can me not being able to enter my house be an improvement???"

Watched DiG! to calm me down (it arrived in the mail yesterday). Thought it was brilliant.

Then somebody had the brilliant idea that maybe my neighbour downstairs at 15a had attempted to get his locks replaced but that they had thought:"15a or 15c", what's the difference. Unfortunately no, that's not it either. So tomorrow I get to call my landlord, I guess I'll keep you all posted. Or probably not, when I find out tomorrow night that my locks have been replaced again.