>>> It's not law just guidance
Wrong.
The Health Protection (Coronavirus, Restrictions) (No. 2) (England) Regulations 2020, as amended by paragraph 2(3)(a)(1) of the Health Protection (Coronavirus, Restrictions) (No. 2) (England) (Amendment) (No. 4) Regulations 2020] states:
"During the emergency period, no person may participate in a gathering which consists of more than six people unless—
(a) all the people in the gathering are from the same household, or are members of two households which are linked households in relation to each other . . . "