Bic, i think I'd leave the bomb and blow up Westminster council anyway. They're a bunch of thieving scroates for introducing the charge in the first place and completely had it coming.
As for the mystery of the vanishing chain... Well its hard to believe that even the most drug addled spazmo is going to spend God knows how long gnawing through an old chain.
I suspect that the person you spoke to at the council is either..
a) lying
b) doesn't know what agents in some obscure part of the council - maybe refuse collection, or road maintanence are up to.
Have you tried talking to the local plod? You are after all the victim of theft, which despite Labour's vigorous massaging of crime statistics is still allegedly an offence in the UK.