Compulsory education isn't mandatory until the term after their 5th birthday (as opposed to simply 'the whole of Reception'. It is age dependent). Unless your child is summer born, you'll need to home educate from the term after their 5th birthday, until the start of Year 1, if you choose not to send them to school until then.
I am a Reception teacher and I advise you think very carefully before opting to take such a route. It isn't simply a case of "they're doing ok academically so they'll be fine starting in Year 1". There is far more to Reception than the good old-fashioned '3 Rs'. Reception is all about settling children into school life. It's very much a continuation of nursery, where there is still plenty of free play, but it's in a more structured environment where they are gradually eased into school life. They learn to share a playground with bigger children. They eat their lunch in a busy dining hall with older children. They attend assembly weekly, maybe even daily depending on the school. This is all introduced gradually, as and when they're ready, and they have that safety net of continuous provision ('choosing time') to break the day up for them. By the start of Year 1, they are use to sitting for longer on the carpet for whole class lessons such as phonics and maths. At nursery, group time will last for no more than 5-10 minutes. In Reception, this will build from 15 minutes to 20 or even 30 minutes at a time. It's a gradual build up.
Reception year isn't just about teaching them the academic skills of how to read, write and count etc. It's about helping them to develop good learning behaviours too. They are learning to take turns and listen in a group. They learn to have a go, independently. They learn to ask questions and explain how they know something. Of course, a child CAN skip Reception and start Year 1 having never been to school before, but they will definitely be disadvantaged by missing out on a gentle introduction to school, before they are thrown in the deep end being expected to participate in an hour of whole class maths.
The teaching of maths has changed significantly in recent years. It's not just about being able to count and recognise numerals etc. The focus is on gaining a much deeper understanding of the number system, spotting patterns and making links. It's about learning key instant recall facts, which will help them to calculate the answer to different problems as they get older without relying on simply counting everything or adding using their fingers (which is where calculations often go wrong). In Reception, we work a lot of subitising (seeing the amount, which starts with simple dice patterns and progresses to more complex arrangements such as knowing that you have 5 if you see a group of 3 and another group of 2, without needing to count). We work on number bond facts up to 10 (so children learn without counting that double 3 is 6, and that 4 and 2 is also 6 etc). If you intend to home educate during the Reception year, you will need to brush up on modern teaching methods if you intend your child to enter the school system at Year 1, otherwise they could end up left behind and very confused if their peers have been taught to do things they cannot do or do not understand.
Likewise, the expectation for writing at the end of Reception is that children can write a simple sentence independently. This will need some input from yourself to get them to that stage, if they do not attend school in Reception, if they are to enter the school system at Year 1. Otherwise, they will be behind and struggling from the start.
There is nothing wrong with home educating. Many people manage it very successfully. However, if you only intend to do it for the Reception year I strongly suggest you read up on the Early Years Curriculum and mirror this as well as you can, otherwise starting at Year 1 will be a huge shock to the system for your child (especially if they attend a school which does not offer continuous provision in Year 1, as many sadly don't).
Many people wrongly see Reception as just a year of playing. Yes the children do play lots, but it's structured play which has been carefully planned out to help them practise key skills. The children are hopefully having so much fun that they don't even realise they are learning, but they are. They're learning an awful lot, in an environment designed to help them fall in love with school and learning. I wouldn't recommend that any child misses that, if they are to enter our school system the following year in Year 1. Nursery to Year 1 is a collosal leap, even for an academic child.
It is not unheard of in my own school for children to start in Year 1 (or later), having moved from abroad with no previous formal schooling in their own country. They catch up eventually, but with an awful lot of interventions both at school and at home. It is a massive struggle for them to begin with. I really really would not recommend it.