The only other airports with current non-trivial general passenger usage I can think of which might be considered to be at risk are Teesside / Durham Tees Valley, Dundee and Prestwick.
Possibly also Humberside, but I imagine the Dept for Transport might be reluctant to see 2 airports in the same region both close to pax service, and access to the North Sea will continue to be required.
I'm assuming Land's End is too remote, Penzance is too small and new, and Norwich is needed for oil/gas rigs.
Are there any others that might be considered to be at risk ?