In reply to all:
Many thanks for all the advice - some of the answers made me realise that having a notion of 'macro' wasn't enough to actually buy something useful. After some frantic research, managed to find a second hand Tamron 90 in very good nick, which was bang-on budget.
Doesn't always get acknowledged, the depth of expertise on UKC, but much appreciated on this occasion.
Merry Christmas to all (I know, now that I've got this one sorted, that mine will be)
Martin