Thanks all - somehow I lost this thread when it got moved.

I agree the Air China price does look interesting. I've usually been reluctant to fly routes connecting in mainland China because of negative reports re the ease of transfer and the way in which I've heard people accommodated in case of major delays/cancellations. How is the on-board service? On flights of this length I usually need a drink or two for reasonable sleep.

The AF flight mentioned was indeed a two-stopper on the way out (CDG and ICN). I'm not fussed about changing twice provided the connections are decent. Unfortunately it's gone up a bit since I posted before, maybe I should have got it then! I think it was 17th-8th when ideally I would be more like 20th-10th, so not a million miles out, and I think Easter might get in the way of going any later for price.

TPE prices don't seem to offer me much for the times I'm after, so looking mainly at HKG and ICN for the potential to switch to budget as well as the Air China option.
Again, thanks for all the help.

Edit:
Some further searching later and there are some interesting open jaws via Fukuoka which could save me some travel time inside Japan as I planned to start that end, even if not as cheap as Air China. I also found a £500-ish routing LHR-ADD-ICN-NRT that I am sorely tempted by just for the sheer absurdity and novelty even if it is nearly 24 hours flying.

How is the service on Air China?
I think it’s fine - and you get beer and wine with your meals.

Personally, I don’t see any difference between changing at CDG or PEK, neither are particularly pleasant.

When looking at open jaw flights, don’t forget to swap around entry and departure airports as flight times from London to FUK might suit you better than FUK to London.

And remember my warning about schedule changes and being able to talk to someone about them before trying to book an “adventure” via Ethiopia. Adventure may be exactly what you get.

FINAL EDIT TO ADD:
To close off my contribution to this thread
Booked ourselves onto Air China for Easter 2020.
Reasons were:
Chinese carrier (Air treaties with China remain in place if Brexit happens)
Booked directly with airline, allows us to negotiate directly if there are schedule changes (likely)
24 hour layover in Chengdu on the way to Japan (yeay!)
Airbus 350-900 on PVG-LGW return flight :cool:
Free seat selection :)
46kg of hold luggage each :D
Free meals and wine & beer on “local” flights (SAS, Air France, Iberia etc only give you food on the transcontinental parts of your journey)

Price was competitive £1,600 for 2 adults and a child on the primo peak Easter travel dates. Which is a hundred pounds above our budget but we get a full day in Chengdu out of it - Win!