Aha! the Mileage Calculator on the website has been rejigged to show 300 / 600 / 900 / 1200 miles for internal UK flights (depending on fare class).
The 250 and 850 have been superseded.
Has anyone had miles for UK flights posted since the changeover? I have had an ORD-MAN and LHR-EDI showing on my account with zero miles for over a week now.