Thank you for the replies and expertise. Chuck, I do not want to use a jigsaw as I am not confident of getting smooth corners, runs etc.
I had clicked on the collar guide bush link on Quillman's post, however I have only ever used router bits that go directly into the router (collet?). The Collar Guide Bush concept is new to me and until I see it in practice, I do not really understand it.
Mike (of Mt Stringer), the Pattern Guide Bit sounds good in that it is of shorter length than the Top Bearing Guided Bits I have.
I really love the smooth finish that I can (sometimes!) achieve with my router. I hope I can get this to work!
I'm away from home for a while, however when I return I shall work on your lines.