17.4 of BAEC T&C https://www.britishairways.com/en-gb...&link=main_nav seems to outline the percentage of refund for non-flight bookings on Avios.

I have not been able to work out how much service fees are payable on cancellation but general service fees are £15 and Avios flight cancellation/change fees are £25 so I'd have thought it would be somewhere around those figures.

Hopefully someone will come along and clarify them.