It is very very unusual to have children accelerated a year in state schools in the UK. And it is often not that successful either.
You have to think long term.
At some point he may well have to repeat a year. There is no guarantee a secondary school will accept him a year early. If you mve house there is no guarantee another school will keep him a year ahead. Equally there is no guarantee a college or university will accept him early.
There is no reason why a state school, esp at primary, can not cope with a bright child. They are not going t be working above the teachers own academic levels after all, not like you may get in late secondary. Instead of fighting to accelerate look at making sure the teachers are offering challenging work.
But also bear in mind that reception IS about way way more than academia. The social side of things are key and also the year ensures the basis is there for ALL areas, not just reading and maths.
There is absolutely no reason for him to gtet bored. i am often sceptical at this anyway because it is pretty unusual to find a child who doesn't enjoy playing with his fiends, esp when there are a large number of different activities around.
And it may look like sand and water and that's it, but it is more. They are learningabout various concepts when using funnels and jugs and mxing colours within the water. They are learning to deal with sharing and communicating with other people, they are learning to follow new school rules, etc.
Oh and bored doesn't have to mean disruptive or naughty either. A very bright child does not have to be naughty. If they are bright they will often have the skills to seek out more challenging activities within the activities that are there IMO. Most of hese receptiona ctivities are very open ended.. One child may be simply happy to play in a shop role play area. Another child may be working out how much different itemscost and what change to give back to the other child. Another may be writing up a shopping list. One might be designing their own item to sell in the shop.
Give it chance.