We can hear it now: all passengers will be required to undergo biometric scanning prior to boarding the plane. Thank you for your cooperation... Question: who does this guy work for?

It reads like a plotline from the hi-tech Mission: Impossible spy films.

Elderly white man in flat cap, brown cardigan and thin-rimmed specs boards plane in Hong Kong and alights in Canada as a young Asian man.

However, the suspicions of eagle-eyed staff as he was boarding were aroused by his strangely youthful hands.

And when the old man didn't disembark the flight at Canada's Vancouver airport, police swooped and discovered an astonishing plot.

In what Canadian authorities are describing as an 'unbelievable case of concealment', it transpires that the young man had boarded the plane in elaborate disguise with a silicone face and neck mask - and switched identities in the plane toilet in mid-air.

An intelligence alert released by the Canada Border Services Agency (CBSA) stated: 'Information was received from Air Canada Corporate Security regarding a possible imposter on a flight originating from Hong Kong.

'The passenger in question was observed at the beginning of the flight to be an elderly Caucasian male who appeared to have young looking hands...