I'd definitely recommend Milligan & Hill physiotherapy. 16 St Helen's Place, EC3A 6DF (v. near Liverpool St station).
See www.milligan-and-hill.co.uk
It costs £41 for half-an-hour and they can usually book you in for the next day. They start appointments at 8am, so you can even go before work if you're in the city.
I've been seeing a lovely guy called Keith Day who definitely knows his stuff and understands how runners think and behave! He's done wonders for my injured hip flexor muscle in just 3 weeks, and has done his best to keep me race-ready for a half-marathon in 2 weeks time. Say "hi" to Keith if you get an appointment with him (although he'll know me as Sonia Storr - not running bear!)
Hope they can help!