Originally Posted by vernonc

My friends just returned from YYZ-BOM-YYZ on these flights.
At LHR, you have to deplane, go thru security and reboard. AC also sells LHR-BOM so its like a 'new' flight with existing pax from YYZ reboarding plus new pax from LHR boarding.
A word to the wise - if you buy duty free at YYZ, ensure it's in the tamper free duty-free bag otherwise it will be confiscated at LHR security