The MBNA Diamond Club has two of the best residual offers in the UK credit card market since its downscaling 2 years ago. Though no longer open to new applicants, it still offers as much as 2.5 Avios per £1 spent on normal purchases and 5 Avios per £1 on flights booked through British Airways, (full earnings chart here).
But did you know there's a perpetual 10% discount on the base fare on British Airways flights if you still hold the credit cards? (The offer has been around for a while, though I haven't written about it before.) The discount applies to flights departing from the UK and the cardholder must be travelling on the itinerary. There is no limit on the amount of times you can use the offer.
To access your discount, simply visit www.diamondclub.org and enter your login details. You should see the discount link prominently after you've logged in.
When you click on the red ‘Book now' button you'll be redirected to your personal British Airways booking page, which will look nearly-identical to the usual form, bar the “MBNA Diamond Club” on the top right. Helpful tip, you can save the link address and bookmark it so you don't have to keep logging in every time you want to use the discount.
Since the discount does not apply to taxes and service fees, the biggest savings will appear on premium cabin tickets. Here's an example of a London – Hong Kong sector in First class with no discount:
And with the 10% base fare discount:
Though I haven't tried it, you could potentially combine this discount with the Proactive Online Upgrade trick to score maximum bang-for-buck. Alternatively, so long as you aren't already in the highest class of cabin on your flight and there's award space in the cabin above, you might be able to upgrade using Avios and still earn back the Avios and Tier Points from your original ticket.
(Hat tip: Ghetto IFE)