32"
http://www.uk-air.net/seatpitch.htm
Edit - The information I have given related to long haul aircraft used by Finnair. However, I have since noticed that Manchester to Hong Kong is not a direct flight, with Finnair, but involves a change of aircraft in Helsinki.
The first leg (Manchester-Helsinki) is operated using an Embraer ERJ-190. This is a smallish aircraft with a seat pitch of 31". The second leg (Helsinki-Hong Kong) operates using an Airbus A340-300 on which the seat pitch is 32".

