>>>>the common-room radios were permanently tuned to either Radio Caroline or, more usually, Radio London (another pirate ship moored off Frinton-on-Sea!).

Thank you - yes, of course - I've muddled - it was Radio London, not Caroline that was off Frinton.
Day girls boasted of having been in one of the cars at Frinton that signalled to the ship
But caroliiiiiiiiiine was the song that everyone associated with the pirates.