I know they are not in the UK but you could get some clear or coloured translucent buttons from arcadeshop.de >
Link You can then LED light the buttons.
You could get a PacDrive from Ultimarc to drive the LEDs >
LinkI am from the UK too and have bought parts from GGG, Ultimarc and arcadeshop.de with no problems.
If you are going to buy an LED controller you may want to take the following into consideration:
GGG LED Wiz:- 32 controllable Outputs
- Can only control 5v devices (fine for LEDs)
- Has 48 levels of controllable light intensity (you can get the lights to fade rather than just flash on/off)
- Is more expensive ($45 = approx £23+shipping and possible import taxes depending on the size of your order.)
Ultimarc PacDrive:- 16 controllable outputs
- Can only control devices up to 48v (external PSU needed for devices over 5v)
- Can only turn LEDs on/off (you cant get the lights to fade)
- Is slightly cheaper £18.47 + postage.
GGG also offer the LED-Wiz+GP >
Link which is a 16 port LED controller combined with a 16 input gaming interface.