It's always worth checking out WT+ prices, though. They are often sold at £100-£200 per sector over the cheapest economy prices, particularly during fare sales. In the last advertised BA sale I picked up a HKG at £299+£150+£150, and a pair of SEAs at £279+£150+£150.
Even though that sale has finished, there are still some low N class (deepest discount economy) fares on BA at the moment on some routes, with WT+ priced at £200 per sector extra.