So I checked the BB again, took off the circlips and managed to prise the BB shells out.
The spindle has a crack in it
I took it down my lbs and was advised that the BB shell would be too small to accept any modern BB if it was threaded, I don't know if this is the case or not?
rmw - Would you mind telling me how much argos charged for the work and do you remember which BB you put in once it had been reamed by argos?
I'm wondering whether I can fit a threadless BB so am currently searching for one small enough to deal with the clearance issues the protruding downtube causes...!