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Standard chartered

Credit Suisse

Barclays capital

Tsuru capital

GSA capital

Alphaheavy

Edf energy trading

... Just off the top of my head :-)

Most quants use functional programming to some degree when not locked down into C++, be it in a specifically funcational language or not. At least in London F# is commonly used in Credit Suisse, Barclays and UBS that I know of. Heard that Morgan Stanley uses it a bit too but didn't sound very widespread there.

Barclays, HSBC and Credit Suisse are three place I know of just based on talking people who've worked there.

In Skills That Matter presentations they sometimes refer to deployments in the city (London finance sector).

You also have some use cases here,

http://msdn.microsoft.com/en-us/vstudio/gg634701#Who_Uses_F_...

http://fsharp.org/testimonials/

It's "Skills Matter" -- they're a company that offers training events, and they handle many of the big F# training events in NYC and London:

http://skillsmatter.com/

Oh right, thanks for the correction.

Novus in NYC uses scala and open sources some libraries (salat)