[andygrif]

Originally Posted by Chris T

You should be able to get silicone sealant that is formulated for bathroom use - have you seen any tubes of it, and did it still say 'not for immersion'?

Yep, checked the silcone out (why does that sound rude?) and yes, that also said not for immersion.

Originally Posted by basa

I'd have quick look on the floor under / around the outlet as the water now probably leaks around the *outside* of the drain pipework !

Strangely there's no leakage on the pipes underneath...which I thought was odd too....so I have no idea where the water is going.

Originally Posted by Robert Atkins

Corning 765 silicone sealant , guarranteed for 20 years. Any plumbers merchants will stock it

Thanks very much...I'll have a search around for that. Much appreciated.

Originally Posted by driver_problems

You should make sure that the surfaces are 'flush' with each other and unimpeded with obstructions etc. Then you should use PTFE tape which will be available at any B&Q store or local hardware store. Ask one of the staff how you apply this tape to the fittings if you are unsure. This should cure your leaking ills

I think that's the problem, the rim on the plughole is not comepletely flush against the basin. But without completely dismantling the whole sink unit (it's all built-in) I think I'm on a loser when it comes to putting PTFE around the pipes under the rim. Or am I missing the point? Plumbing is not my strong point (can you tell?!?!)