There is lots of talk of reducing the 2-metre rule to 1-metre. It seems to me that in an open area and ignoring the effects of wind, the risk from a given amount of virus will follow an inverse square law: 2 metres is 4 times safer than 1 metre. However the risk is equivalent if the source of infection is four times lower.   So I am comfortable with a 1 metre rule when the number of people in the population infected is around one-quarter of what it was when the 2 metre rule was introduced.

In a confined space the calculations are really complicated, but after a while you would expect the virus to be roughly evenly distributed around the space, and so 2 metre or 1 metres does not really make a difference. Until the uniform distribution is reached, it will be some blend of the two situations.