Thanks for all the advice guys. In the end I geared down by 1 at the back, removed the half-link and then filed the dropouts deeper and slightly forward (by about 3mm). Worked a treat, though perhaps it's a little too tight now (there's a slight noise on the drivetrain now and it doesn't coast as well as before). Still, it seems that too tight isn't such a bad thing, and if needs be then I can always get the file out again!
Thanks for all the advice guys. In the end I geared down by 1 at the back, removed the half-link and then filed the dropouts deeper and slightly forward (by about 3mm). Worked a treat, though perhaps it's a little too tight now (there's a slight noise on the drivetrain now and it doesn't coast as well as before). Still, it seems that too tight isn't such a bad thing, and if needs be then I can always get the file out again!