Drill the fucker out from the outside with a diamond drill bit would be my best bet on that one. It sounds like you need a new lock anyways, if it was the c/l motor playing up you should still be able to open it with the key.
I work for a motor dealership in sunny England so if you need a new lock give us a shout and I might be able to get a good price for you (even with the price of shipping added on, apparently the UK has good prices for car parts.)
I've gotta work tomorrow anyhows so I might get a price for you.
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