Is homework legally enforceable in state secondary school?

Well if your DS avoids having to do anything outside class (with your blessing), that will stand him in very good stead for being independent at University or Work.
Go ahead.

I'm not sure how old he is, not doing homework in year 7 and 8 might not make a hell of a lot of difference, but certainly by year 10 he'll need to be using 'his' evening for homework and exam revision. So best he's already in a routine of doing it earlier on in the school.

I don't suppose school uniform is legally enforceable either, but they will have a policy for non compliance the same as they will for homework. If you choose that school you are signing up to their policies by default.

I think school can enforce it's own expectations, including detentions if work is not done.

My DD2 had almost no energy left after school, but luckily her schools set limited homework for lower sets, and then the pandemic came anyway.

Unless your DC has SEN I suspect you need to find a way round this, as just refusing homework won't end well.

Options as I see them (if no SEN)
. Use a homework club in school for homework
. Don't fight at home but let school impose whatever sanctions are necessary
. Talk to school about any other ideas they may have
. Look to move schools to one with a different approach
. (Home Ed)

Not legally enforceable in the sense that there is legislation that mandates homework completion, but if there is a school policy then the school can act if that policy isn't followed. This would mean that if homework is required to be completed according to the policy and hasn't been then they can follow the documented disciplinary process, if it continues then they can follow the escalation, that could mean eventually suspensions/exclusions or permanent exclusions.

I say this to clarify that this specific thing I am asking about need not negatively affect other pupils.

Except it does if your child doesn't write the essay I set for homework, and doesn't do it in detention either. Because then someone else plays the same game...

...and the upshot is that I now have set essays in lesson time instead so I now have less direct input time.

Do you mean: Can the police be sent round if your child doesn’t do his homework?! No!

If your DS didn’t do my homework though, he’d find that there were a number of occasions where he couldn’t participate in the next lesson - if I’ve set reading homework, it’s so we can begin the next lesson with a discussion of what’s been read; if I’ve set a written task, we might begin a lesson with some peer or self-assessment of that. So his learning and progress would be negatively affected in the sense that he’d then miss out on chunks of subsequent lessons.

And if they had no choice of school?

say this to clarify that this specific thing I am asking about need not negatively affect other pupils.

Well if he hasn't done the research for the next day's lesson and the teacher has to waste time explaining stuff to him, or he hasn't done his bit for a group project etc, it could well impart on other pupils learning.

If you don’t support the school and what they are doing you should have chosen a different one.

I doubt it's legally enforceable when it's not legally enforceable to attend school. but why is it taking over 'our evenings', it's his homework. And really, he's not there all day. School finishes at 3.30

Why is his homework dominating your evenings?

Teacher here, I sincerely doubt it.