Formal primary education in the England and Wales starts from the age of 5. (i.e. all children starting in 'Year 1' will be 5 years old). However the usual practice is for a child to join their primary school at the start of the term in which their 5th birthday will fall. So, for example, a child whose birthday is in February will start school in January. For the first two terms that child will be in the 'Reception' class, before going into Year 1 in September.
Formal education is not compulsory prior to the ages indicated above. Some private providers merge the concepts of 'day care' and 'education' so that a child might have a place at their centre from soon after birth all the way through to the start of formal education. So there's no fixed age for the start of 'nursery school', play school', 'kindergarten', 'pre-school' or anything else.
However all 3 and 4 year olds are now entitled to 12.5 (or, in some cases 15) hours of free early education each week. Most parents probably take it up but it remains optional:
http://www.direct.gov...onClasses/DG_10016103
Incidentally, this country is largely out of step with the rest of the world. In most other countries formal education doesn't start until the age of 6. In Scandinavia, where formal education doesn't start until age 7, the British system is seen as akin to child abuse.
Chris