British Airways has for a long time offered a discount on their tickets if you cash in some of your Avios. Typical savings are:
£10 for 1,500 Avios
£30 for 4,500 Avios
£50 for 7,500 Avios
You can now save £100 if you exchange 15,000 Avios.
If you are Avios rich and cash poor this is not too bad a deal. You still earn full Avios and Tier Points if you use the discount.