For all of you looking for a good hairdresser in London, I know of this italian guy, named Luca (I don't have his last name) that works at Vidal Sassoon salons.
I'm not sure if he still is there, since last time I had my hair done by him was 2 years ago and at the time he was alternating work between London and Italy.
He did a very good job and advice me not to get my hair quemically treated but to use the phytology products (even though we were at a VS salon, he didn't try to sell me any of their stuff).
You could try calling and asking for him at the 60 South Molton Street, tel. 0171-4918848.
Do keep in mind VS salons can be quite expensive.