The mid-century “caff” diner, once a staple of London life, is rapidly being swept into Formica heaven by trendy bistros. Among the few holdouts still feeding Westminster’s cops, security guards, and bureaucrats, is the 1940s Regency, an elegy to another age in yellowed white tiles and bolted-down plastic chairs. This isn’t a gastronomic treasure (the fryer is in heavy use, white bread heaped high, sausage a food group); it’s an anthropological one. Big-value food including homemade meat pie is prepared with lightning speed and your order is jarringly bellowed so that you can come fetch it. For another marvelous caff, see E. Pellicci in East London.