With great relief I can now say my air bag system is reset and the light is out, and the MoT is done. But it was not from the cables and software recommended on this forum. After showing the garage the correct ecu port they were able to talk to the ecu with their machine, which is a 'Snap-On Modus Ultra' but with using leads from their previous diagnostic machine, a Solus Probe (the engineer thinks that the Solus Probe would have worked too, but cannot confirm that). This is great because I tried to download the trw2scan and was told a FTD2XX.dll file was missing and I thought "Here we go", round and round trying to get the software downloaded, but the garage phoned today and told me the good news. Perhaps the cables I have bought will be useful for other diagnostic work later.
So the conclusion, your local garage can reset your air bag if they have the right machine and know the correct ecu port to enter.
Remember, the light not going out is an MoT failure, so get it fixed or, If you're happy for the air bag to be disabled, remove the bulb remove before putting the car in for MoT (You can't take it out after an initial fail as the tester knows the air bag is not funtioning, if there is no light in the first instance then he can't know there is warning system at all).
Love and pace to all.
20VT, Aston DBS, Ferrari F355