Levelling floor

[Khan]

Just converting a utility room to an office/ study. The old floor slopes pretty consistently from one long wall to the other dropping about 40mm over 3m but it does have a few depressions about 5mm deep. What's the best to fill this in with, self leveller will just run to the low side but its too thin for a screed mix? Would tile adhesive work?

 

[Doing it for the kids]

You could try self leveller in stages

 

[Sharpy]

10 years ago I was asked to rectify a builders poor work on a renovation. 3 rooms had 3 inch to zero screed required to sort it out. I screwed tile batten to the floor for levels, packed up or shaved thinner where required.
The screed mix was whin dust/ flakes (5mm) sand, cement, and a lot of plasticiser. The 3mm bit at the end was done with self levelling compound. Worked fine, battens are still in!