Thanks for the advice. I decided to try to get a cheap splitter - my local motor factors were out of stock, and suggested I could get a "cheap & cheerful" one at What!, but What! didn't have one either. So I decided to try without.
The first side was straightforward - a few whacks with a lump hammer and the old joint was separated.
The second side is giving me some problems. The nut holding the track rod end to the steering knuckle started to unscrew but now the stud from the ball joint is turning with the nut.
My options are to somehow grip the stud whilst unscrewing the nut with a ring spanner, or to cut off the nut (nut-splitter ? hacksaw ?). Any suggestions for the best method ?