British Airways is offering 40% off economy awards originating in London (although it apparently works from other cities in the UK as well) booked by November 2 for travel through March 20 to a variety of destinations.
Since you still pay full taxes, including exorbitant fuel surcharges, this isn’t as great a deal as it might seem. You’ll often pay a substantial portion of what an economy ticket would cost without the availability of a paid ticket and without earning miles. However this can be especially valuable for: