Thanks Hotel21.

The garage that did the gearbox service changed the ATF/Filter on my 02 320CDI and it was a top job (sometimes I can't even feel the gearchanges). However, I know there is a dipstick for that box so the level is checkable.
The faults with my miggy box are the same before and after ATF/Filter change which MAY (as some have already said) suggest a new solenoid is required.
However, your diagnosis may well be spot-on if the garage only replaced the amount of fluid drianed from the box, and that amount was insufficient to enable the box to operate.

The garage (bodyshop) that did the g/box service are a competant outfit and have been unbelievably kind to me in the last few years (helped me out on two accident claims - one fault and one non-fault) and I'd hate to go back and ask them to take another look at the box. I know that when changing the ATF/Filter on my 320CDI that they ran the engine and went through the gears to flush torque converter...
So is there a way of me establishing the oil level in the box without returning the car to the bodyshop?
I really appreciate the help on this forum and am very grateful to be around fellow miggy owners who are so willing to offer help.
Many thanks.
Paul.