That seems odd, Shed. BA's Reward Flight Saver deals are very good. You should have been charged only £35 in cash, plus the 9k Avios. The only criterion for eligibility for the reward flight saver is that you have generated 1 (yes 1) Avios in the last 12 months.
Maybe your Avios account has been inactive? Worth checking with BA anyway, as these RFS deals are one of the best uses of Avios at the moment.