Its not so much about trust or training bubbles.
Its about protocols - and I have no idea what they are
You'll have players staying in hotels in London.
If released, they'll have to travel home. That could be a pretty long journey for some, so bay involve stop overs, or at least food stops.
Then they'll be staying in a different bubble at home - with family /house mates / other.
Then into a separate training bubble......
Then the same in reverse the following week to get back to England training.
There could well be protocols in place to limit that happening