Sensible Transatlantic won't work from Luton at present - the runway is too short.
Stansted is not easy to get to from Cumbria, and your Norwich family were probably the only Norwich residents flying to NYC that day! Also, Stansted has an unfortunate history of transatlantic failures - they must have failed for a reason.
Just look a little further north and you will have your answer - Birmingham and Manchester still have TA links, and both serve major business centres.
I expect that for the foreseeable future, no airports in the UK will join the TA club.