how and where do I collect seeds from shirley poppies

Try getting the book Growing from Seed (RHS Practicals) it is full of into on how to harvest seed, sow seed everything you need. ISBN is 978-0751337228 and it was published by Dorling Kindersley

As for your Shirley poppies they have what looks like a pepper pot at the end of the flowering stem once the flower has died back. This is the seed pod, if left alone they will naturally sprinkle their seed every time the wind blows on them. To collect seed wait until the pod is brown, not green, cut off with pod with part of the stem, tie a paper bag (not plastic) over the seed pod and hang upside down somewhere cool and dry. Give the whole thing a gentle tap when you go past it and you'll soon have lots of seed in the paper bag. Poppy seed is very fine and black.

Thanks moongrower I'll be looking out for that book.
Next year I hope to have loads of shirley poppies they are beautiful.

Yes they are Scardycat... not something we grow as our garden is alpines, rock garden plants and woodland plants but they are beautiful