I’d suggest revisiting the design and going for infill constructional slabs, raising the concrete up, dropping the insulation down, and having the UFH pipes in the slab (have a look at insulated raft foundations on google for context 😉. No need for screed then.

We’d need some details of the thresholds to add other comments!

Your internal floor level is 375mm above external ground level. That won't work for a level threshold. At thresholds you can run the insulation and screed to the outer leaf, with perimeter insulation of the screed and DPM detailing required. The won't be an inner leaf of timber frame.

Too late to redisign I have got doors and windows being measured next week and fitted early dec. Going to have 5 coarses of bricks forming the exterior plinth its a detail for removal of interior blocks showing dpc and insulation that I need .I have got main entrance with low threshold ,rear door and 3m patio doors . 150mm pir and 65mm screed bring me up to just below dpc.

You can cut out the 2 timbers at the threshold.