I bought the ticket

I bought the main ticket and I was able to change the itinerary to the order that I originally wanted. So the plan is now:

30 Nov - London to Melbourne via Singapore
(this is good because now I can be in Sydney for christmas with Caroline)
31 Jan - Cairns to Auckland
(I had to pay £130 extra to fly from Cairns instead of coming back to Sydney because this puts the total mileage at 30,700 and the limit for this ticket is 29,000.)
24 Mar - Christchurch to Singapore
03 Apr - Singapore to Hanoi
18 May - Seam Reap to Hong Kong via Singapore
29 Sep - Delhi to London

This is with Virgin, Singapore Airlines, Air New Zealand and Silkair. I can't do the flight from Khatmandu to Delhi on this ticket because those airlines don't fly that route. I could have gone Khatmandu to Mumbai but I've been told that if Mumbai is the first place you arrive in India it's a bit of a shock to a westerner and it can put you off India. Instead I will book a local flight from Khatmandu to Delhi which should cost about £88.

Also I couldn't book the flight Delhi to London on 29 Nov because the booking system would recognise that as 29 Nov 2005 (when I want 2006) so I will change it nearer the time. With this ticket, I can change the dates I travel on but its' expensive if I want to change the routing. The total cost of the above including taxes and insurance was £1,645.

The other bits in the itinerary will be either via train (Beijing to Ulan Baator) or local flights (Chengdu to Lhasa).