Hi,
We have already replaced the washer, and the seat - and the tap still drips... are we missing something here ?

Thanks for any and all responses.

Assuming you replaced the washer with they correct one and did a good job on the seat packing is all that's left. HowStuffWorks "Replacing Faucet Packing" (http://home.howstuffworks.com/home-improvement/plumbing/how-to-repair-a-faucet3.htm)