Well just booked the following which may be of use to someone:
LHR (PE - upgrade to J with Avios) - MCT (First) - DOH (Buss) - BKK (Buss) - DOH (First) - MCT (PE) - LHR
Used Avios to drop the BA PE ticket down to £471
Upgrade additional tax £53 + 20000 Avios per ticket
QR MCT - BKK £616
Nets me 90 + 60 + 140 + 140 + 60 + 90 = 580 Tier Points for around £1100