I use Rosemary Watson's Gumpaste recipe. It is very strong and holds up to a lot of handling. You can find it here:
www.sugarbouquets.com
go to ideas then to lacy cakes and you will find it.
IMHO- Sylvia Weinstock's book is not worth the money. The recipes are seemingly wrong and incomplete as are her directions for flowers. A great book for sugar flowers is Cakes by Design by Scott Clark Wooley. This book has been worth it's weight in gold. He has it available on his website.
www.cakesbydesign.cc Anything by Alan Dunn is also very good. Rosemary Watson also has a video that is very good if you are a visual person.
Hope that helps.