Hubby did his in Leighton trained for 4 days then did his test in the 5th day in Northampton as it was the test centre with a an appointment I will ask him which company he went with and let you know.
There's a place in Hollingdon don't know what they're called though. Turn right at the crossroads towards Stewkley then left on the corner and they're on the right hand side just before you get into the village with big signs so you can't miss them. Only a couple of miles from your yard