I don't know about their cocktails, but Bar Elba in Waterloo is a nice rooftop bar -- good vibes for a medium-to-large social event. The Alchemist (like Scott suggested in another comment) has very interesting weird cocktails, but personally, the novelty wore off after a couple of visits as the cocktails themselves are... OK.
Other nice cocktails bars that I can recommend are Callooh Callay and Cahoots.
I don't know about their cocktails, but Bar Elba in Waterloo is a nice rooftop bar -- good vibes for a medium-to-large social event. The Alchemist (like Scott suggested in another comment) has very interesting weird cocktails, but personally, the novelty wore off after a couple of visits as the cocktails themselves are... OK.
Other nice cocktails bars that I can recommend are Callooh Callay and Cahoots.