I am not sure how this would play out, but there are some cheap fares from Shenzhen Airlines from LHR to BKK in November. I can see it for less than £300.

The interesting thing is that when I eventually tracked down the booking fare (had to go to Expedia.co.th to find it!), it books into P for the LHR-SZX leg...that's currently listed as First discounted on the A3 accrual chart (hence 150% of miles). My calculations for the whole trip make it 18,972 miles! I wonder how long it will take them to update the chart!