Just tried calling the DVLA on that number. When I eventually got to speak to a human being, she said she couldn't tell me whether the original number was still available, and that I needed to call 0300 123 0883. I did this, and after another interminable conversation with a computer, got through to someone who told me that this department only deals with personalised numbers for sale, and the number that I needed to call was the original number, and that the previous person had given me faulty information. At this stage I gave up, defeated by bureaucracy. I am just going to assume that the number is available, and go ahead and apply to re-register under this number, and only if this is rejected worry about what to do next.
I can't quite understand under what circumstances an original number would not be available. The personalised numbers department told me that they only sell numbers that are brand new and have never been allocated to a vehicle, even in the 1950s. So if the original number was not available, what would have made it so?
Thanks - Rowan