all the steps in the flight must be equal

Scruff, please ask your builder, "Which version" of the building regs is he referencing...and which part....

as the 150mm is a MINIMUM height.... and as for the other dimensions, they  all depend upon their application. such as domestic, institutional, industrial etc etc etc...

therefore LEC....

document "K" (2013 rev) Part 1 , table 1.1 (pg14-15) states private stairs, not accessible to the public.... rise 150MM MINIMIUM to a 220mm MAXIMUM..
  and  going 220mm MINIMUM with a 300mm MAXIMUM...

sorry if I seem a tad rectal, but I spend lots of money each year/ when ever a new amendment is released to keep my regs fully up to date... I hate being advised incorrectly by damn stupid architects and council officials... whom only seem to whoosh over the basic's of any reg, and do not look it to ALL of the options if, X Y or Z apply...

I have even tripped (sorry for the relevant pun) up recently an architect,, whom it turned out was 2 sets of updates behind the world...

I trust this helps people...

to quote section 1.1

"SCOPE: the guidance provided in this document covers internal and external steps and stairs when they are part of the building: see approved document M, Section 1 (for buildings other than domestic dwellings)"

subsection :

"Construction of steps" Must have level treads on steps, ensuring the rise and going are consistent throughout the flight, and are in accordance with table 1.1"

oh, white in off the black  

Provided the cill does not have an over hang of more than 70mm from the brick/blockwork outwards then it is not included in the dims, so the 200 rise is fine...