Rode to the station on the Brommie this morning and the reassembled wheel seems to be fine. Hurrah!
However, I realised that the problem with the chain is that it's for a 7spd (3/32") and the 3spd sprocket seems to require a 1/8", so getting the chain to engage with the sprocket was a bit hit and miss.
I went up to Bikefix during my lunch break to see if they could get me some replacement pawls for my singlespeed wheel. They didn't know, so phoned Brompton. It wasn't good news. So I'm stuck with
gears (spit!) for the time being. Oh the ignominy! (Mind you, until I replace the knackered gear shifter, I can only use two of the three gears anyway, so it's not so bad.
)
I bought a new 1/8" chain while I was there and fitted it, so the ride home is sorted, at least.
d.