If it's a contracted shift you are definitely entitled to a paid rest break within a 6 hour period. Meal breaks can be unpaid. There can be a grey area, and may be worth getting union advice about it, with regards to dealing with emergency breakdowns, being on call or on standby etc, and might depend what's written in your contract. When I started working in the NHS in 1995, right up until about 2012, we provided standby (on-site) cover and on call (from home) cover. We'd work our normal shift, say 8 hours, from 9am and then if you were on standby, you'd effectively be working until 9am the following morning, with the next day off. If you were on call, and got called in from home (road accidents, or lots of trauma/emergencies), on occasions you could end up working all day, all night and your shift the next day too. Get advice.