I suspect this price increase might be related to the additional £8.90
Airport Cost Recovery charge that started appearing on flights from Heathrow last month. This avios price rise will ensure that the customer rather than BA will bear most of the cost of this on short haul RFS flights.
The price before today's changes of an economy return zone 1 peak RFS flight was 18000 avios plus £1. Now it is 19500 avios plus £1 or 18000 avios plus £9.