I think this might vary from area to area. Where we used to live "nursery" was either a day care (from 0-5) or it was a nursery year attached to a school, so in effect a pre-school attached to a school. It differed from the pre-schools where I now live in that it was mornings or afternoons, but you did all 5 and started the september before you started school - it was slightly more school-like. Advantages were that it shared grounds with the school and some assemblies and sometimes used the big hall so that the next step to going to school there wasn't such a big leap. Also good to get to know a group of peers going to school with you, although nursery doesn't influence whether you get in or not.
Where I live now only one school does a nursery-year, but is as above, a year in advance, all 5 mornings (or afternoons) and has a uniform. Most people use pre-schools which funding kicks in from the term after they are 3, and many take from 2yr 9 months so you can go earlier than exactly a year before school (or later). These are often more flexible with days, so for example my daughter went 2 mornings a week for one term, then 3 mornings and will do 4 mornings a week for her actual pre-school year.
Pre-schools and nurserys vary enormously as to whether its mainly a hall with free play equipment in it or a set structured day with french, ICT and ballet lessons. The ethos can vary a lot as well. Ours is privately run but not profit-making which I very much like. It has a lower child-adult ratio as they put money into extra staff and the staff are older and really care for the kids. One I visited looked like they tried to employ young cheap staff as a profit making exercise.
I would suggest asking around at mums-and-toddler groups in the area to get a feel for the local groups, or asking on the other site (nm) for local opinions. The family information service near you should be able to help too. Nothing beats visiting (with your child).