DD (3.7) is in state pre-school in Monaco. The system here is identical to the French system. I have no idea what the system in the UK is like, but here are the basics of ours:
Pre-school is not mandatory but it is very unusual for a child aged 3-6 not to go to one. Cost entirely paid for by the state. We were only asked to pay EUR 50 for the entire year, as "participation" in costs.
Pre-school is not supposed to teach reading/writing, but they will apparently be able to do both by the time they leave this school.
There is one teacher & one teacher's assistant per class. There are 28 kids in DD's class, which came as a bit of a shock because we were told at inscription that they would be 17-18 in each class. Apparently there was a cut in their funding at the last minute and number of classes had to be reduced.
First year (age 3 to 4) is only mornings and 4 days a week (Wednesday the exception) unless both parents are working, in which case they keep kids for lunch and put them to sleep for two hours in the afternoon. DD is there between 8:30 to 11:30.
Most days, they do various kinds of rather messy art, learn songs, and spend lots of time on the outside terrace on bikes and with lots of toys.
Is there anything else you would like to know?