Our schools federation has gathered the key worker children from three primary schools and one secondary school, put them all together in the secondary school and used teachers from each school on a rota system. As many others have done. They did that with a few days notice. On top of ensuring home teaching - DS has just finished a language test, is working on humanities, did a week long project for English, does a maths test every day and a weekly science project. His PE teacher has sent through a PE test each week - measure 20 metres, run it 5 times, record your time etc., His school sends a newsletter home every couple of weeks and they're running 'virtual school clubs' - a cookery club where you can send in photo of something you made, a photography club (speaks for itself), a film club where you write a review of a film you've watched, a book club (same), and a sports club (!) where you take a photograph of yourself doing an individual sport and write about it. I think that's very innovative!
1400 of the secondary school children are now on line every single day.
The children who are in the key worker school go to an outward bound school during the holidays (mini-bussed from the secondary school) so the main school can have a deep clean and the kids can have a bigger area to run in. So the idea of using another type of place isn't beyond the scope.
I think the issue around using town halls and museums etc though is that it can only be temporary. The town hall, leisure centre, museum in our town will be returning to work eventually. And probably by the autumn. Which means that the schools in our area could get everyone back (in theory) within the next few weeks - assuming we have enough teachers/TA/support staff to cover nearly 3000 primary/secondary school students now split into classes of 15.
But come September we'd lose many of those temporary classrooms and would be back to square one.
What's needed is an injection of cash to allow schools to rent porta-cabins IF they have school fields (and a lot of those within inner cities were sold off years ago). You could even use marquees in the summer months. But you need something solid for winter. We need permanent structures by the autumn term if every child stands the chance of returning to school properly.
You can't rely on other organisations spare space because it will only be 'spare' whilst they're in lockdown. As soon as they're back, they'll need the rooms again. I don't know many places around us that could have a full week of classes in rooms. Even our church hall has WI, yoga, meetings etc happening (normally) every week. Do they kick those groups out indefinitely? Because we have no idea how long our kids or teachers will need to work within these constraints at the moment.
As for Denmark, I didn't see the programme so can't comment on that, but DH has a client in Denmark and was speaking to his counterpart there. She has two children in primary school. They go to school form 8.15am to 11.15am each day. That's it. Three hours. She's panicking about what happens when her company calls her back to the office as there's no after school clubs at the moment in her area so she'll be stuck as her DH is a key worker so can't work from home.