Looks like there's a pretty broad sale. If you sign-in to BA EC and have your location as UK, there's a lot of cheap F fares.
Quick glance for NA:
ATL from 1969 gbp
BOS from 1898 gbp
LAS from 2029 gbp
NYC from 1853 gbp
YYZ from 1696 gbp
All ex-LON. I didn't check the dates but this seems to come up annually. LON-SFO gets you ~60K RDM on Alaska w/ MVP 75K bonus, or around 45K w/o it.