Originally Posted by
Davee58
Try clicking the "Multiple Destinations" link above the "From" airport on the KLM booking screen.
This will allow you to enter a three part journey on a single ticket, such as:
MAN - BKK - (1 week in Bangkok)
BKK - AMS - (3 days in Amsterdam)
AMS - MAN
If you take the AMS stopover on the
outward journey you
might even save on the evil UK departure tax.

I really expect that it would be cheaper to just buy MAN-AMS-MAN on one ticket, and AMS-BKK-AMS on another.
I don't think the UK APD can be avoided by the above suggestion. UK APD can be avoided if any stopover in the UK itself is less than 24 hours, but on tickets that depart from the UK, it is levied regardless. A ticket from UK to wherever will carry the appropriate APD for the final journey, regardless of where any stopovers are made, and regardless of how long the intermediate stopover lasts. The key is to not have a ticket with a longhaul destination included issued in the UK at all.
You'll avoid having a UK longhaul APD factored in buy buying the longhaul (if it even is a longhaul that is under consideration by the OP) by starting that ticket in AMS.