My experience has been in the rail industry where the rest periods between shifts have been very long established. My understanding of the work time regs is that there is a rest period of 11 hours between shifts every day plus a 24 hours rest period at least once a week. Therefore 11 hours on Monday, Tueasday, Wednesday etc and at least 24 hours at the weekend. This can of course vary according to the industry you work in so in simple terms there must be a minimum of 11 hours between shifts and 24 hours at least once a week. If your take 24 hours the 11 hours is lost as the longer rest period would cover it. Hope you get what I'm saying as I'm a bit confused myself now.

"Under the Working Time Regulations 1998, regulation 10, a worker is entitled to a rest period of 11 consecutive hours rest in each 24 hour period during which he works for his employer.

However, there are a number of special circumstances in which the entitlement to rest periods does not apply, for example, where the activities involve a need for continuity of service or production or where there is a foreseeable surge of activity. Also, if a shift worker changes shift, it may not be possible for them to take their full rest entitlement before starting the new pattern of work. In such a case the entitlement to daily and weekly rest does not apply"

http://www.hse.gov.uk/contact/faqs/workingtime.htm

Don't forget that if the 11 hours cannot be provided due to company committments then compensatory time must be factored in.