American Express is running a promotion with both of the mega Westfield shopping malls in London.
Until 31st August, which does not give you long, you will receive a £20 statement credit when you spend £100.
Unlike most Amex promotions, the £100 spend does NOT need to be at one single store. You can shop at a mixture of stores, on different days if necessary.
Frankly, the easiest thing to do is to buy £100 of gift vouchers at a participating outlet. Waitrose is participating, for example, so buying £100 of John Lewis / Waitrose gift cards (yes, they have finally started doing plastic gift cards and got rid of the paper vouchers!) is an easy one.
I won’t be back in the UK before the 31st, unfortunately. If I was I would be tempted to register every Amex card I can find and buy £100 of Waitrose vouchers on every card, given we shop there every week.