Hi Louis,
I believe it is not a requirement by the UKBA or Airport Custom but by the airline especially if the person who bought the ticket is not flying. Not often they check when purchased by person travelling. It is normally stated on airline's website or emails. In my case last year, below is what was stated in my e-ticket:
For security reasons, the following are required upon check-in or ticket reissuance,
failure to produce these documents may result in denied boarding:
1. Photocopy or actual credit card used for the online purchase(s).
2. Photocopy or original photo ID of the credit card holder.
My husband sent me a scanned copy of the two mentioned documents. I was fully aware to keep it safe and secured. Good thing I had it with me because the lady asked for it when I checked in. And of course, it was returned to me immediately.
Congratulations to you and your wife!Best wishes on your life together here in UK.
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