I used a YST threadless BB and it was pants, it kept coming loose which meant I had to keep removing the cranks to tighten it up.
I bought a Velo Orange Grand Cru Threadless and it was much, much better. It never came loose, but even if it had, one could tighten it with a lockring spanner, without removing the cranks. Overall the quality felt excellent (as with all VO products).
Not heard of that brand before, looked at a couple of reviews and they seem positive, just going to find a uk supplier and check the price.
I contacted Bob Jackson cycles, they wont do a sleeve and rethread, they offered to cut the shell and weld it tighter and rethread but no guarentees for about £30 which I'm not keen on, or replace the shell completely for £110 - which is way to much to spend on an old frame project.
So considering that I'm unlikely to do massive miles on the bike I think the threadless is probably the way to go.
JM that is a good idea, I could try it with a scrap one to see if it will fit.