That's probably the best idea anyway, especially as you would then avoid UK Air Passenger Duty...
If I was going on my own, then I would be perfectly happy doing it that way, however the Wife just wants to get there ASAP (understandable) but she's not happy about the prices online. With a pit of puersuasion I might get her to come round to the idea. Just got quoted £1,446 for the two of us from Brussels, Lufthansa Brussels - Frankfurt, Air China Frankfurt - Beijing, then to Chengdu. Return is more straightforward with Hainain Airways Chengdu - Beijing then onto Brussels. She might just buy that considering PRIV to Brussels is pretty cheap, as is the PRIV Euro single Newcastle - London.
Might also try getting DFD's to Amsterdam, then KLM from there but she doesnt like travelling by Ship!
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I got booked up a couple of weeks ago coming the other way from Hong Kong to Newcastle for April/May. The prices for most of the flights via London were just stupidly expensive so opted for Emirates via Dubai. I accept however that EK do not fly to Chengdu so also probably not an option for you.
As a rule I tend to book about 3 months in advance if I can but obviously it's not always possible.
Also don't forget the taxes etc on many flights are higher than I have ever seen. For example from HKG to NCL via LHR I was looking at over £600 with around £300 of that in taxes and surcharges.
Good luck in your hunt.
Yeah, I noticed that the taxes have seemed to rocket. Its shocking, only a few years ago I got quoted loads of flights for under £500 and all on National Carriers. I think we might have to settle for flying from a European Airport and using train to get there, which will add onto the journey time (not a problem for me but a big problem for my Wife) and the added time and expense of her having to apply for a Schenzen Visa