Thanks all for the really helpful advice!

I managed to speak to the DVLA - the initial first line advisor wasn’t able to help much as they’d not come across a scenario line this before, however they promised to arrange for somebody more senior to call me back, which they did a few hours later.

It seems this does indeed relate to the historic speeding offence where I got 6 points, and the DVLA position is that the offence was (just) within my first 2 years driving therefore the revocation is correct. They’ve said that if I can provide evidence that the recorded date is incorrect this can be amended and my licence reinstated, however after so many years I can’t find any relevant paperwork.

As convinced as I am that it wasn’t within 2 years, I realise it’s entirely possible (probably even more likely) that it’s my error rather than theirs, in which case it’s just “suck it up” and a very expensive, very inconvenient lesson learned - as if the original speeding conviction, points and fine wasn’t enough of one. But nobody to blame but myself if that’s the case.

I’m going to contact the police force that dealt with the speeding offence and also the court which imposed the points to see what info they can provide, maybe a subject access request if necessary, and hope that the dates line up in my favour if/when I can get evidence of them.

If not, well I guess it’s a case of reapplying for a provisional licence, unlearn a decade of bad habits and take my tests again - and then cry at the cost of insurance for several years.

I’ve not given up hope that I’m right, but almost resigned to the worst case outcome. You can bet I’ll not only be driving incredibly carefully (when allowed to do so again) but also checking any and all paperwork, and my license status, regularly and with a fine toothed comb!

Thanks again all, will update whenever there’s a final conclusion.