Total confusion over Covid restrictions

Having just got used to the idea that for Christmas three households can get together inside to celebrate, the UK Government announces that London and many other cities will be categorised as Tier 2 locations once lockdown is lifted on December 2. And under Tier 2, two, let alone, three households are barred from meeting inside a house. So, for example, if friends or family are planning to join together for more than the stipulated four days over Christmas period, are they allowed to stay or what if they arrive, say, on December 20 and want to stay till the New Year? Grant Shapps, the transport secretary, announced separately that if people coming from abroad have a test five days after arriving from overseas they won't need to be in self-isolation. But if they arrive in a Tier 2, or worse still Tier 3 area, they won't be allowed to join up with other households anyway, so the relief from self-isolation is meaningless. I don't know whether every other country is announcing contradictory and confusing restrictions or restriction-liftings for this Christmas period. But as far as I can see, I don't know whether to lock my house and stay put like a hermit for the whole of December or have open house!