Entered UK with Vietnamese passport but flying to Canada with a Canadian one

Question

I'm having doubts on which passport to use for my coming flight from the UK to Canada. I have Vietnamese and Canadian dual nationality, and previously entered the UK on my Vietnamese passport with a visa. If I travel to Canada using my Vietnamese passport, then I need a Canadian visa on it, which is impossible. But if I check in the flight with my Canadian passport, then as there's no exit control in the UK, it's hard to prove to the UK border I'm not overstaying on my Vietnamese passport? In this case, how can I fulfill the entry requirements for Canada and at the same time let the UK border find out I have left? Can I book my flight with my Vietnamese one and later show both passports at the check in counter? Will they allow me to board on the plane?

Answer 1

What you show the airline and what you show Immigration doesn't have to be the same. As you said, the UK doesn't have exit controls. So when checking in for your flight to Canada, you show the airline both passports: the Vietnamese passport with the visa and the entry stamp. And the Canadian one to show you don't need a visa. Then on arrival in Canada, you show your Canadian passport.

The UK will know you have left – the airline, having seen and recorded your Vietnamese passport, will notify UK authorities.

Answer 2

If I were you I would follow dda's advice but assume that the airline failed to report your departure correctly. This means that you should retain what documentary evidence you can of your departure from the UK and/or arrival in Canada. If you can, get a paper boarding pass.

You probably won't need this evidence: the UK's departure controls are very porous. For example they will not record your departure if you cross the land border into Ireland (and probably also not if you take the ferry or even fly there, but I do not know the details). It not an offense to fail to have your departure recoded. Your absence of a departure record won't be particularly alarming since a significant number of entry records won't have been matched to a departure.

So the only way this is going to affect you at all is on a subsequent entry to the UK, where they may ask you when you left and whether you can prove it. If you show your boarding pass for the flight to Canada that ought to be the end of the matter.