Employment law question re: working hours

[D-Angle]

I have ended up working on shifts where I am at the moment. There are 2 main parts to the pattern: early shifts 8am-2:30pm one week, and 1:30pm-8pm the next. Part of the pattern means that we work 13 days in a row(Monday-Sunday, then Monday-Saturday), then get Sunday off before doing another 5 days.

My question is, I have heard that 13 days is the maximum amount of days you can be asked to work in a row, but you must be given at least 2 days off afterwards. Does anyone know if this is true? And if it is, do they mean 48 hours or 2 calendar days? I finish at 2:30 on the Saturday and start again at 1:30 on the Monday, so it's actually 47 hours. Does anyone know who you would take this to that would enforce it, bearing in mind there is no union of any kind in the place at all.

[jamesw2000]

I believe you can opt out of the working time regulations, which would remove the need for a two break - you're employer would have got you to sign a form saying you had agreed to opt out of this though.