rgwm - ok it seems to be working now.
The power connector block may have been the problem. I took it off, noticed a loose pin in the row of four contacts and prised it out a bit for tighter contact, then roughed up the metal contacts in the bulb holder before plugging the connector block back in. I used a long umbrella to hold the break pedal down, jamming it against the door pillar (as no one else was daft enough to want to stand out in the cold for half an hour while I went though all the possible checks) and the brake light came back. I wonder how much Alfa would charge for all that faffing? I also found a dud fuse in the cigarette lighter/power input, replaced it, and that is back working again too. Thanks!