MH metal but KL code
 

I'm flying MH in business class AMS-KUL but on a KL code. Am I right in assuming that I'd have to earn fairly useless Flying Blue points rather than BA avios/tier points?

Correct.

That would be my understanding too, though I haven't got precise experience of this. However I do know that if you quote your BA number "on the off chance", it is quite probable you won't get anything at all.

A few Flying Blue miles can be useful for some purposes, so it's worth having a wee kitty of them stashed for a rainy day. Note that they are changing their system at the moment (greater availability, lower charges, but more miles required outside Y, to give a brutal summary). However they are letting people redeem at the previous rate if done by telephone by the end of this year.

Indeed, with flight with KL code and MH metal, your only options are MH Enrich or AF-KL FB. To credit to BA, you would need the flight to be both MH coded and operated, to credit to another Skyteam FFP you would need the flight to be both KL coded and operated.

Thanks folks. Just what I expected. I connect on in KL for a flight to RGN and I'm going to try to switch over FFPs in KLIA so I can get those 40 tier points on BAEC.