Beyond multiple people confirming that Cummings warned him (shit, how is Cummings the good guy in this?), wasn't the UK in lockdown around that time? So like, parties/gatherings of all sorts were banned? Doesn't he know what happens at his house?
Man, if only us regular folks could benefit from the, "We're stupid and didn't know this wasn't allowed. We're very sorry so we can't be in trouble!"