So the Luton TMZ was the thin end of the wedge!
Now we have one of the largest most empty pieces of CAS (see the LAA response to the last change) demanding a TMZ is an area where presently there is no transponder requirement - or much prospect of an ATC service.
There does seem to be an unpublished policy to insist on a TMZ under virtually any circumstance where radar 'might' be impaired.