Some detail from the court in the local rag here :
Black Lives Matter protesters fined after admitting City Airport trespass (From East London and West Essex Guardian Series)
They don't appear to have been "fined" as the headline says but charged costs - and then given a conditional discharge.
I see that "Charges of being unlawfully airside were not continued with". Why ever not ? It's a pretty open and shut fact that they were. Does it mean that all those notices on perimeter fencing about dire penalties if you enter an airport are completely irrelevant ?