Mollygo
3 households. I’ve mentioned this before. If I invite 2 (immediate family) households, to ours, there would be 8 adults with one retired and the others all working in various contexts (not from home) including teaching and hospitality, 1 student fresh from Uni, and 2 children. 3 households isn’t any more sensible, no matter how good it sounds.
I think what everybody is failing to work out is that the restrictions aren't trying to keep you "safe". They aren't trying to make the chance of you catching Covid zero. They're trying to reduce probabilities.
If there are eight people in your house, the chances are reduced compared to if there are 30 people in your house. And especially compared to going to a concert with 1,000 people. That's it.