Me personally? No I wouldn't.
If you're really pushed I'd go 75mm concrete with a trowelled finish and 5mm self-leveller.
But you'll need a good, well-compacted layer of hardcore under that.
I've just read your other post.
Why not:
Do it right, do it once!
Decided to go for compact hardcore, sharp sand on top, DPM, and then 4/5 inches of concrete, then the insulation and UFH and all that jazz on top. No screed. The theory being having just concrete is better than having just screed.
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