Garage Separating Wall

Hi all,
Trying to sort out a separating wall for a garage conversion, could use some guidance on the wall diving new heated space and remaining existing garage area. New heated space will have door into it from house, garage will retain garage door into it, there will be no access through new separating wall.

Currently shown on detail a fire resistant stud wall on brick plinth. Can anyone confirm suitability of this brick plinth? I would assume it would be best ‘belt and braces’ approach rather than studwork on DPC/M existing concrete floor and also, in terms of retaining the concrete screed. Or would this be overkill? Perhaps even, it would be better with single course of block (saving labour time)

Additional info: existing single brick wall upgrade will be insulated studwork with 50mm cavity and roof will be existing pitch roof upgrade with rafters insulated between and under.

Would love some feedback on this.
Cheers, Simon.

It's a brick plinth because it still has a garage beside it, otherwise spillages of oil or fuel would compromise a stud wall if it was sat at garage floor level it would thus be a fire hazard.

Thanks, with regard to the ceiling will it be suitable simply to have the ceiling above heated area insulated between and below to prevent fire risk or would the separating wall have to continue through roof void to underside pitch roof rafters? I would assume that rigid board between and under as well as x2 layers of plasterboard would be sufficient, otherwise maybe an additional layer of mineral to fill over rafters?

Best to ask building control, see what the inspector wants. I think the easiest solution would be to board the garage ceiling and the converted part with a fire rated loft hatch in the garage. The last extension I did, the inspector wanted one layer of fire resistant plasterboard, then normal plasterboard and then plastered. It used to be 2 layers and then plaster, so just ask the inspector if he/she is happy with two standard plasterboards and plaster.