Many thanks, Mad-Jock.
Just 'phoned the CAA and they confirmed I've got an embedded IMC with my CAA ATPL, so that looks a reasonable option.
Lifetime PPL looks dubious, and they'd have to check their microfiche records, as I'm not sure whether I can find the original.
They suggested I write in documenting exactly what I have, what I want, and they will make an offer. Depending, that is, on EASA.
EASA?