Cellar Floor/ steps query

[u/Regular_Departure_53]

We are moving house, and our plan is to develop the already tanked out cellar room (with external door) as a Kitchen/ Diner.

As part of this, we will be installing floor insulation/ floating floor, so adding around 70 to 80mm to the cellar floor.

This will obviously raise the floor below the staircase - my concern is that this means that not all stair treads are even, so it will not meet building regs.

What, if anything, are the options here (house is 1850s, stone cellar stairs part of fabric of the building)

Thanks for any thoughts!