BA removed the refund of fuel surcharge from non-refundable fares some time back - which does seem somewhat underhand - if you're going to vaunt it as a surcharge for fuel used, then refund it if the fuel isn't used. Or do the right thing and bake it into the base fare, in which case you're well within your rights as an airline to retain it when a pax cancels. But c'est la vie.

These days, you should get back the government taxes, plus anything levied under passenger service charge type lines.

IIRC, refund fee is around £30-£50, and on an MFU you should get the miles refunded.