Is there any reason why children should not repeat a school year?

And thinking about it the early years issue would be particularly discriminatory in terms of those with additional needs, in terms of support, early intervention, diagnosis etc.

The problem is you will have two big difficulties at each end of the scale. At school entry level what happens to those children who would be entering school in September. Some will currently be in nursery education, some won't. The time they spend in nursery will vary considerably. If they are to remain in nursery the number of places would need to be expanded hugely in order to give a uniform nursery experience, and as there will be younger children coming in, places, space and staff would all need to increase. The legal position would need to change as well because children currently must be in full time education after their 5th birthday.
Then at the top end what happens to universities and colleges? The courses they currently offer would be empty for a year. They would suffer substantial financial hardship, many are already struggling because of the lack of overseas students. It might lead to a reduction in the courses being offered. Then how many young people at the top end would drop out because they wouldn't want to repeat the year?

I suppose the issue is what happens to those children who are waiting to enter school of nursery and reception classes don't move on.

Of course we have the massive issue in the UK of teacher retention due to horrific work conditions (I am not talking about covid here, just the usual s**t teachers face). As you point out Dinahmo, this would add to the issue of having one extra year group in education.

I have been saying this for a few weeks now.

The key issue is that state funded education ends at 18. I absolutely think for school children of the pandemic, that this should be extended to 19.

I work in private education now. I have an 18 year old starting a course for 16 year olds. I have a 15 year old who has a VERY difficult past stepping back a year to give her more time to aclimatise to school, before hitting IB Diploma (A Level equivilent). At my previous school, I had a 20 year old in a class of 17 year olds.