Nigel,
I did this several times when I was younger and it always worked out prettywell. Granted, I think I used whatever I had around the garage (probably satin Rustoluem). It definitely was NOT the proper paint to use but once the overpowering smell went away (about a week with windows down ion the garage) it lasted for years since it was not an interior piece that the body does not comes in contact with. At least I knew to tape off and cover the interior and a good chunk of the exterior of the car and be patient with spraying thin coats and letting them dry before applying another.
There are much more appropriate rattle can upholstery dyes out there now so go check out what's available. I would start with SEM first and see what they offer.