Apparently there's a new 'no-frills' company that's going to start operating out of Gatwick from next October, if that's not too late for your purposes..?
Friends of my parents have gone to China with The Travel Department. One on a 9 day trip to Beijing only and the other to Beijing & Shanghai..both gave them the thumbs up. Have a look at their website
If you don't want to do a guided tour try Trailfinders. We backpacked in China in 2002 and used Trailfinders for our flights. We flew with British Airways to Beijing and home from Hong Kong.
If you wanted to do the trip independantly then you shouldn't have too much trouble getting around Beijing and Hong Kong as english is fairly widely spoken...the fun starts when you go off the beaten track and have to moo or make chicken noises in restaurants
I have used the travel department for many holidays. However on my last two holidays with them I felt that their standards were slipping, not by much but enough to cause annoyance. They don't deal with complaints very well either, a view shared by some "regulars" on the trip. Having said that I will be giving them one more chance.
We went to China in 2000 and coukd find no one in Ireland to go with and went with Virgin Holidays from the UK, they fly to Shaghai direct from London and then we went to Bejing with Air China (an experience!!). Virgin were fantastic, we were upgraded to a suite in Bejing and have gone with them on a number of trips since. The only drawback is that you have to pay in Sterling. But do check their website. My parents also fo with the Travel Departement on holidays a lot and have nothing but good things to say about them.
http://www.intrepidtravel.com/destination.php?region=china - can be booked direct or through Trailfinders in Dawson Street.
also [broken link removed] - they are a little pricier than Intrepid and again can be booked through Trailfinders. One of them has larger groups than the other - can't remember which. The sites should tell you. You also have an option to travel independently. This is tricky in roman character-less China. You would really need a local agent to make bookings etc for you.
I visited China in 2004 and went with a UK company - www.travelsphere.co.uk - who have been bringing tourists to China for over 25 years. Guided 2-week tour visiting Beijing, Xi'an, Shanghai and a Yangtse River Cruise. Saw most of the sites (forbidden city, terracotta soldiers, yangtse dam etc) and found it very useful to be part of an organised group (as my mandarin leaves a lot to be desired!!).