Well done for pursuing.
It will probably take another voice to support your concerns with the DVSA follow up in order to get a favourable response. Safety-related recalls normally require evidence of accidents or statements of failure where accidents were narrowly avoided. Lawyers won't be interested unless there is a claim or enough weight of claims to be made, and Audi will be about £ damage limitation. Is it worth contacting someone like the AA or RAC or some other lobbyist ? Maybe not.
I suppose it could be argued that if Audi USA has a recall, it could either be for a safety or environmental (likely) reason. If Audi UK is using the global 7 year warranty claim path now without recall, they have clearly taken a commercial view rather that it is not a safety issue, and would surely have to share this with DVSA ?