Try a search on this, as it has been asked before.
But Main Test centres are
Bournemouth
Bristol
Cranfield
Oxford
I think Perth in Scotland too, but dont quote me.
You want to find out How much of the course is Sim, S/Engine or Multi,
Where they do the tests,
Number of aircraft approved for IR tests (for back up if yours goes tech!)
Positioning costs to test centre
Any training at Test Centre Airports,
Any other students you can pair up with. (Back seating is VERY useful).
Availability - Will you get regular consistency or frequent gaps due to busy instructor etc.
Also try to speak to previous students as they will no doubt have a "customer orientated" view of their experiences there
Best of luck!