Thank you for all your replies; this is certainly an interesting topic.
In terms of funding, I agree that there would need to be checks in place so that pre-school funding (for example) does not ending up costing more if the summer-born delays starting school. Although on this example, and I appreciate that this is only anecdotal, our son does not attend pre-school yet, even though he's 'allowed' a place by the government. And our daughter only attended pre-school for one morning a week before starting school - even though she is a September child. She was happier that way and didn't want to go any more than once a week. I guess what I'm saying is that the type of child we're talking about - that is not ready for school at the age of 4 - is less likely to be in nursery or pre-school at an early age either.
As for academic achievement, these articles (just examples) point to research that makes interesting reading:
Does it matter in which month you were born?
www.anthonymillard.co.uk/independent-thinking/does-it-matter-in-which-month-you-were-born
Children born in summer are '13 months behind classmates' in maths, a study has found
www.dailymail.co.uk/sciencetech/article-2237523/Children-born-summer-13-months-classmates-maths-study-found.html
School odds stacked against summer babies, says IFS
www.bbc.co.uk/news/education-15527145
That said, I think the point about whether spring-term babies might become the 'disadvantaged' ones (in general terms) is a good one, and the only thought I have on this is that even if the choice to delay some 4-year-olds was allowed, not all parents would make that choice, so in effect, the spread should remain the same. And even though some children would be a year older than others, if developmentally they are close (i.e. the August-born babies that we all hear about who go on to do really well - and who are ready for school), there shouldn't be a problem for teachers...?
TalkinPeace2, you have added to this discussion precisely what I wanted to avoid here - an anecdotal example and sweeping criticism of anyone who wants to make a different choice to the one you've made - or whose individual child is different to yours.
The whole point about choice is that you assessed your own child as ready to start school, while someone else might assess their child as not being ready. You say your child would have been bored if he hadn't started when he did - yet I can say the opposite about our daughter. She is thriving in school as a September-born baby - had she been born two weeks earlier and forced to go last year, she would have been very unhappy. Yes, she may have 'coped' but I am grateful that she's able to enjoy more than that.