Typical NHS trust paramedics work a 37.5 hour week. The hours are averaged over a rota which can be anything from 4 to 24 weeks. The number of actual days worked will depend on how long the shifts are and the frequency can vary depending on how the rota was designed. Some rotas have whole weeks off, others never have more than three days in a row off. .
The shift lengths can vary from 6 -12 hours, although typically the actual working time will be 30 minutes less than this as unpaid mealbreaks are the norm.
However before getting a rota line it is often necessary to spend a period on relief. Whilst on relief the average hours worked is still 37.5 but is planned on a week to week basis, some weeks way up and some way down.