Before the latest lock down the 'rule of six' came in. With some exemptions, for example if your household was larger than 6 people.
However - from the 29th March " outdoor gatherings (including in private gardens) of either 6 people (the Rule of 6) or 2 households will also be allowed"
I assume this means the rule of six doesn't apply to two households? Before lockdown it was a bit of a logic puzzle, involving leaving some of my household at home to meet with another household!