I'd love to work 3 x 16 hour shifts! 48 hours pay but with 4 days off per week sounds just great to me!
(Back in my student days I worked 7 x 16 hour shifts for 10 weeks in a row. 112 hours per week certainly helped my bank balance! I've also worked 24 hours on, 12 hours off for long periods).
However the current regulations make working three 16 hours shifts
on successive days, at the same times an illegal employment practice because of the requirement to have 11 hours rest between the end of one working day and the start of another. However three 16 hour shifts in a week is not illegal, per se, as long as the shifts are spaced far enough apart to provide 11 hour rest breaks. The rules on night-working might also be relevant.
For full details, see here:
http://www.direct.gov.uk/en/Employment/Employe es/WorkingHoursAndTimeOff/index.htm
Chris