Level stairs

Can anyone point me in the right direction with regards to building regs for tolerances to levels across treads.
Thanks in advance

 

http://www.staircases.org/regulations.htm is this any good for you mate..

 

Thanks but not quite what i need.
My problem is that the stairs across the tread are not level and rise by upto 25mm on the handrail side .I thought they had to be level or within a tolerance eg. + /- 2mm across 1m tread but i can't find anything published.Any help would be grateful.
Cheers