So here's the update and the answers to my own questions!
After the ABS and airbag warning lights came on while my Missus was coming home last evening, I called around a few mates to see if they could recommend anyone who could have a look.
The recommended mechanic asked if I could bring it in this morning. Five minutes into the trip, all the warning lights began coming on one by one, with three loud beeps and a flashing (!) light being the last.
The speedo dropped to zero, the clock and trip meter vanished. No indicators, probably no stop lights either and I'm now needing to make a right turn on a busy road to reach my mechanic.
The moron behind began to overtake and we were almost all toast, but for the oncoming car swerving onto the verge. There was sufficient time and impetus after Jensen Button had passed to swing the now-dead car into the turn, made all the more difficult by a complete lack of power steering and brakes.
V. dangerous and not to be recommended....
Thanks for all the advice. As a result of the posts, I knew what to say to the mechanic, who then changed his tune from 'needs a new one' to 'I'll see what I can do with the existing alternator'.
In all, the car did about 35 miles and started 7 times.