I was a CSA for about three years until promotion.
The contract is quite convoluted (I'm still not sure I completely understand it!) and refers to a 35hr week but also a number of rostered Sundays, payment for which is 'rolled up' together in the basic pay.
Overtime and rosters vary from station to station. OT is rarely offered at our station and is in the form of banked hours. Bank Holidays get a day in lieu on top of time worked, except Christmas Day and Boxing Day which have the option of extra payments.
Roster is earlies (0700-1500), lates (1500-2300) and nights (2300-0700) with the occasional spare (1100-1900). Pattern is normally seven on and two or three off, with four off after nights.