I'm new to growing veg but I have just received an order from
http://www.nickys-nursery.co.uk/
They were very quick, I sent a cheque and received the order about 4 days later!
Each pack of seeds came with a plant label and they e-mailed me to ask if I got the delivery ok which was a nice touch.

Having not grown the seeds I can't verify the quality but I went on price and the fact that the web site was easy to deal with.