I think
BahrainLad (or it might have been someone else), mentioned Milk and Honey.
Got a good review:
Winner Best Bar 2004
Milk & Honey oozes exclusivity with the unmarked door and ring-for-entry arrangement of a Prohibition-era speakeasy. The interior is fantastic: a jazz age affair of dimly lit booths, a low ceiling covered in diner-style aluminium and a business-like corner bar area, lit like a Hopper. Staff are the model of professionalism, and the cocktails they prepare are sublime (not too bad at £7-£8.50). Discounting the caviar and oysters, bar snacks barely total up to half a dozen choices, but they are fantastic, particularly the spicy fishcakes (£6). And the best thing of all? Despite the air of exclusivity, anyone can visit. Just phone in advance and make a reservation. It's a simple caveat, but it keeps the tourists at bay. However, be warned, M&H also operates as a members' bar; come 11pm, when you are asked to leave, members can sit smugly and linger until 3am.
It's 61 Poland Street, in Soho.
Streetmap.co.uk Link.
Any other ideas?