Reception is a very different experience to pre-school. There is learning - in particular reading and basic maths - and I would genuinely worry about any child joining in year one. But it's also about friendships -my son is about to start his third term of reception. He has close friends, with whom he has close bonds, and there are also children in his class that he's not interested in playing with. I think it might be hard to go into those established groups.
Most schools have separate play areas for reception kids.
There are lots of holiday clubs available to help working parents.
If he's born in December he will be one of the older children in reception - all the more reason to bite the bullet.
Finally, some families find the jump from reception to Year 1 is actually much sharper than the jump from preschool to reception. Year 1 is much more formal in many schools, so might be even more of a shock to your child.
Just a few thoughts though - you will know what's best for you and your family,