Trapped hot air in loft

You need to install vent slates/ tiles

I think your roof is it not classified as a warm deck roof ! It will help if air circulation from one side to the other side of the roof can be done just by replacing the fascia board with a vented one However this will not sort out the problem! Dormer flat roof needs 150mm thermal insulation as a kingspan or coletex , also to allow 50mm air circulation gap between roof structure and insulation My concern this will it help to solve the problem

The loft has not been insulated property as all that heat is getting in through the roof. Brick and block will not let that amount of heat into any building so it's getting in from above

Roof vents works for the roof the roof is sealed inside the loft area with insulation plasterboard and skim plaster VELUX roof lights have vents that can be left open with out fear of rain to circulate clean fresh air you can also lock the window open on dry days if you wish. You should have trickle vent on your windows to dormer.

Vented roof tiles high and low on roof plus round vents in soffit boards

Put vented facia and also slate/tile vent.