Usually on my return to UK I go to the check in desk and ask them to change my passport info for the leg of the flight to my flight to Britian to my British passport. I use my Canadian one to leave the UK and fly into Canada. I show them both passports.

Summary
I have a Malaysian and American passport with the below situation and appreciate thoughts on below especially on return to America because of visa requirement.

Situation
Passports – I have both Malaysian and American passports
Visas – Malaysia requires visa to visit America but America does not require visa to visit Malaysia or second country Hong Kong
Policy – I understand America doesn’t care that I have a not allowed Malaysian passport but Malaysia does not allow me to have an American passport and will make me choose passport if discovered

Travel
Book ticket in America – use Malaysian passport
Check in at starting airport in America – use Malaysian passport
Departing immigration in America – Not applicable
Arriving immigration in Malaysia – use Malaysian passport

Book ticket – do I have to book 2 one way tickets instead of round trip because I have to use Malaysian passport to depart Malaysia because I don’t have visa for Malaysian passport to visit America and switch passports in intermediary country Hong Kong on the way?
Check in at returning airport in Malaysia – use Malaysian passport
Departing immigration in Malaysia – use Malaysian passport

Intermediary country Hong Kong arriving immigration – switch from Malaysian to American passport despite flight data?
Intermediary country Hong Kong departing immigration – use American passport to match arrival and departure passport?
Intermediary country Hong Kong check in – use American passport

Arriving immigration in America – use American passport

Scenario above doesn’t even get into the complications of having to renew Malaysian passport in Malaysia because I don’t have a green card to renew Malaysian passport while living in America. I appreciate anyone’s advice. Thank you.

It seems odd that the Canada rule on leaving UK with the Canadian passport would apply. What I’d recommend is contacting the UK embassy for the best course of action but most likely it will be to show both passports when you’re there. Do confirm though for the official information. Hope this helps and if you get a response and don’t mind, updating here with what you were told may help other travelers in a similar situation. Thanks!

Leaving Britain you have to use Canadian passport (new Canadian rules) so I also have to use Canadian passport to leave Canada to come back to Britain there is no opportunity to swop over to British passport this results in going into the foreign national queue even though I have British passport. Is there anyway around this?