S76H
You'll find the "SRATCOH" rules at the end of
http://www.caa.co.uk/docs/33/CAP670_A05.pdf The entire document is about 2.2MB in it's entirety but I think the bit you're interested in is Annex D (?)
These are the basis upon which rosters are compiled and service is delivered in the UK. Different ATSPs may use these rules different ways according to the service they offer (or are contracted to) e.g. closing ATC for fatigue breaks or providing relief or indeed augmenting the maximums to give relief every 90 minutes etc.
1261 - I thought OPM calculated minimum rest breaks according to where you were sitting (i.e. SRATCOH position or Enhanced Relief) and accrued breaks of 1 per 4 or 1 per 3 minutes worked respectively (?) [In any event, there is a debate to be had as to whether the way this is calculated is or isn't in the spirit or letter of CAP670 - but I'll leave it to those who know more (just about everyone) to have it ....
Hope this helps,
RT