Hi, it's not a TMZ. It's Controlled Air Space and is covered under equipment schedules published in the Air Navigation Order. It also requires an ATC clearance and is a known traffic environment. ATC can permit non equipped aircraft to enter.
The CAA Policy is:
A TMZ is normally established for overriding safety reasons, where the airspace classification would not ordinarily require aircraft to carry a transponder. Where the case can be made a TMZ may also be established within controlled airspace. The establishment of any TMZ shall be in accordance with the Airspace Change Process contained within CAP 724, the Airspace Charter, and the associated guidance published in CAP 725, the Guidance on the Application of the Airspace Change Process.
No application has been made to change the Scottish TMA to a TMZ through the Airspace Change Proposal and I can see no reason to do so as existing legislation is adequate.