Where to find a decent recording studio in London?

[ababa]

I need to record a video/audio tape (CD or DVD)and submit it to somewhere. I'm looking for a decent recording studio with a decent (mini-)grand piano. I also need an independent certificate which states that my piano performances on the tape are unaided and unedited. The tape must be of good quality and recorded professionally.
(1)Where to find such a recording studio in London (with a good grand piano)?
(2)How much will it charge?
(3)How to get an independent English letter which can certify the authenticity of my performances (unaided and unedited)?