i've tried every evening session and weekend lane session. like other posters have said it can vary, but i regularly find myself too slow/fast for one lane or the other. it's not the end of the world, instead of swimming for sustained periods at a regular pace, i now do things like swim really hard in the fast lane and then relax a bit in the middle lane. i do find the weekend allocation of lane sessions disappointing, my old leisure centre at mile end would regularly have half the pool laned off and half left for leisure swimmers and families, and it's the same size as dulwich. for those of you don't mind hopping on a bus, the camberwell leisure centre has re-opened, and has a separate swimmming area for lessons and tots. it's colder than dulwich, but not as busy and the lane sessions at the weekend are longer.