That is a Red-legged Shieldbug (Pentatoma rufipes), Les.
Some nicely different angles there. Always a tricky species to photograph due to the hotspot reflections.
You were sort of correct with Forest Bug but that is an old name for it. However, that name will still be found in any old identification books. My old (2005) Shieldbug book still uses that name
Do you use the British Bugs website? That is the ultimate source for any bug identification. The shieldbug section is here
http://www.britishbugs.org.uk/galler...atomoidea.html
There are some books available and most general insect books will have a good shieldbug section but as far as I am aware there aren't any actual identification keys. So it is mostly a case of personal knowledge and starting your quest with 'it looks a bit like . . .' Moths are another similar problem; although far worse!
Thanks Geoff i just use google