I can remember (in my student vacations) working 24 hours on, 12 hours off every day for 6 weeks! (I've even worked 36 hours on, 12 hours off, for extended periods)
24 hour shifts remain legal, as long as there is a minimum of 11 hours from the end of one shift to the start of the next one (and you get an uninterrupted break of 24 hours once per week, or 48 hours once per fortnight). Further, your only legal entitlement to a break during the 24 hour period is to a single (unpaid) break of 20 minutes.
The 48-hour weekly limit is irrelevant anyway since (when calculated over a 17 week period) you only average around 42½ hours per week.
http://www.direct.gov...sAndTimeOff/index.htm
Chris