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http://www.jrplumbinglondon.co.uk/
JR plumbing was recommended to me before by someone here, I think it was @andyp? Never personally used them but I have spoken to them in a couple of hairy situations and they sounded reasonably priced. Reason for not having gone for them is purly because I have always managed to twist a mate's arm who usually works in North London at the 11th hour.
Thanks mate, doesn't look like he comes near us but might be worth a call...