It turns out that requisitioning is perfectly legal under the Civil Contingencies Act 2004.
I'd have to check, but the Conservative Party probably voted in favour of that Act. If anyone will have voted against it, then it will have been Jeremy Corbyn.
The Conservatives have certainly had long enough to repeal it. They have never done so.
Of course, that applies to the property of people who live here full-time and pay the tax. Never mind to the property of people who don't.