I genuinely don't understand the last thing in your post Ron, in that I don't understand why Dept for Ed hasn't already issued a detailed set of principles and guidelines to be followed by schools in preparing to have kids back. Or is it that they have, but the heads don't agree with it?
All I can see on Gov.uk is a one-screen set of trivially basic, now-wash-your-hands type recommendations for schools. And headed with the warning: "This guidance is of a general nature and should be treated as a guide, and in the event of any conflict between any applicable legislation (including the health and safety legislation) and this guidance, the applicable legislation shall prevail." What bloody use is that, right now?
Although every school will be slightly different in the way it applies sensible and practical risk mitigations, I'm guessing that there's scope for 90%+ commonality of approach and this is where having a top-down mandate makes sense. LEAs, where appropriate, should certainly be consulted so they can feed in local factors if any, but there's going to need to be a fair bit of imposed standards from DfE or there will be confusion and potential chaos when parents start asking why their school is doing things one way when another school across town has a different approach.
Unfortunately with Gavin Williamson in charge (yes, the bloke known as "Private Pike" when he was Defence Sec) I don't have high hopes this will get sorted quickly.