In the US even when there are swimming lessons in schools, they're often dramatically understaffed (from my point of view) -- one teacher, no lifeguard, for 30 students. There are several recent incidents in the US of immigrant kids drowning in school lessons.
How was the staffing done at your school or elsewhere in the UK?
The class was usually split up in to groups of about 10, depending on age / proficiency. There'd be a teacher leading each group.
There would also be the lifeguards from the pool. If I remember rightly, this was at least two, if not more -- there always seemed to be one sitting up in the high chair, and there always seemed to be one patrolling the pool edge.
It was a 25m pool, and while the school was there it was closed to the wider public.
How was the staffing done at your school or elsewhere in the UK?