You might call GClean 0845 1284045 who are a Vauxhall based cleaning company. They did a brilliant job on a very grubby cream carpet I had in a tenanted property, and, so far, have proved reasonably priced and reliable for end of tenancy cleaning.
They will have the kit to do a sofa, though don't know what they would charge for a one-off job like this.
An entire year has gone by since I contemplated cleaning my sofa and today is the day it's happening!
I called Gclean (thanks, Sarah), but they were booked until mid-October. So instead I went for Service Master (thanks, TLMJJ) and they are currently in the process of cleaning it. I'll let you know if they do a good job...
For those that are interested, I'd just like to say that the sofa looks really good now. Not quite brand new, but very clean looking (and smelling!), which is a relief (I didn't fancy forking out for a new one!).
Note, however, that I was told it would be dry in 4-6 hours and it is still damp this morning, nearly 24 hours after the clean took place. Hopefully I'll be able to sit down this evening.