Sizzles - your child does not need to be in education (be that at school, or home educated) until the term after they are 5. In reality, most people choose to start their child at school in the term after they are 4.
Even then you have choices. Generally, when you have been offered, and you have accepted the place, you can then ask to defer the place until the term after your child is 5. If they are an Autumn born child, this would mean them starting after Christmas. If they are spring term, they would start after Easter. However, if they are summer born, they need to start in their same school year in orde to keep their place, so would need to start after Easter.
If you choose not to start your child until the term after their 5th birthday and they are summer born, then it usually means them missing reception year out all together and going straight into year 1. There are several difficulties with this, one of the main ones being that there may not be any spaces available in year one as you would need to apply a year later so may not get any of the schools you prefer.
For summer born birthdays, you also now have the right to request that your child starts in reception in the following year (ie. They start in the reception in the term after their 5th birthday). However, this is something which needs to be agreed by the Headteacher and is not an automatic right. Again, you would need to apply the following year, and do not get an automatic place.
I realise it's complicated, but it really is down to parents to start asking the questions. it would be pointless the local authority writing to all the parents of children in a particular year, as there is no way they would be able to track them all down. Instead, posters are displayed in schools, nurseries, GP surgeries, libraries, children's centres etc. in other words, all the places where parents with children are likely to go.
I hope the information in my post is useful (and accurate!), but it really is worth speaking to the admissions department at the local authority to check before you make any decisions.