13 hour shifts and no break!

Nurses are working 13 hour shifts in the community in a local Trust. It runs from 7 pm--8 am. The nurse may or may not get a break, depending on the demand, as theya re on call, so in effect could be driving 13 hours without a break, though they are told to take a 20 minute break after 6 hours to "keep legal". To add insult to injury they ae paid 12 hours as the reasoning is some nights they are in the office a long time if they dont get a call out. Nevertheless the Trust advertises the service as 24 hours, so they are getting an hour free. Is this legal--or safe? Some years ago, when we did 10 hour shifts, the same case was brought up and won--we were paid for the full 10 hours but a new manager has reversed this.

GS