Just for the record, and to help others, I thought I'd conclude the problem.
A few days ago my gearbox (auto) went into Emergency Limp mode. I took it to the BMW Technician that I use, and by this time I had received my replacement ABS unit which he had diagnosed as being the problem for the cutting out, and ABS and ASC dashboard lights. He tried to change the ABS unit but it was a slightly different part number (it was cheap so worth a try), and the car wouldnt accept it. He then put the old ABS unit on and recoded it and since then it has worked fine - no ABS and ASC problems.
On the same visit, the code was read for the gearbox problem, and pointed to a rear wheel sensor. This was changed and gearbox now fine too.
I can't help wondering whether, as suggested on this site, that the ABS ASC problem was the rear wheel sensor all along ?
Either way, sorted now. And thanks for the help guys.