The 26,000 mile ticket ex-London is L1,179 (or L1,289 in high season). Ex-Canada, the same ticket is C$3,999 (or almost twice as much). I don't understand why you would have this issued in Canada when you are starting in London?
The Canada exception allows one to purchase a UK departing xonex in Canada at the UK price so she would be able to purchase at the UK price. I have no clue about the itinerary or if the OP is actually doing something other than an xonex.