You are right. We stayed in a hotel over summer half term in London, we booked a slot and got 90 mins but actually it was fab. We had the whole pool and surrounding seating to ourselves! But as you say, they are few and far betweenI think also places that still have their pool open are rare. At the moment you have to book a slot to swim in most places or otherwise the pool is closed. That was the case a couple of weeks ago when I was looking.