According to my borrowed copy of The Lefties Guide to Britain ed. Peter Clark (Politico’s, 2005), p. 301, the grotto was also used ‘in the 1950s by a group of Leftie writers, artists and politicians.’ In the true, teetotal, puritanical tradition of the British left, the guide goes on to say:
‘Nowadays it is a bistro, but tea for two may be enjoyed for £2′.