Sounds like it needs the wheels balancing. I used Abbey motorsport, but not local to High Wycombe.
Whenever I've changed my wheels and tyres over, I've always used Adams and Page in Cressex industrial estate. They have low trolley jack for cars with clearance issues on the ramps.
I have just had my alignment done at Nissan HPC in Tunbridge Wells on a hunter machine.
It drives fantastic now but cost £200 inc Nissan tax but I am sure you can get it cheaper elsewhere just make sure it's a hunter system. and make sure they get all the readings as close to centre as possible.