> Anyone got any recommendations on where to buy
> one in the UK

Most of my G6s are the older type, and I have had need of Maplin part
no. GL35Q in the past (these are 'T100' fuses). If you have the newer,
toroidal, power supply, then according to the link Florian supplied,
you are going to need GL55K, which is the 400mA rated one. If you have
anything other than a bog-standard G6, check that link *very* carefully!

Tim