Hi hope you can help.....firstly 2 things to point out before others do 1) we are not able to apply any floor levelling compound due to other steps that go in and out of this room 2) The builder was unable to bring the step any further in due to the head height of the opening. 

This is a 200 year cottage that has a new extension - when taking out the connecting doors we found these old 'setts' that were clearly the external entrance to the old cottage.  They are of course now part of the inside of the house and we need to lay carpet.  without using floor levelling compound what it the best way to grind (I assume) these down and using what tools? Thanks in advance

You can use compound to simply fill in the low spots, however if your high spots are already too high then grinding a scutching is the only way (apart from remove and replace)