Hammer: As a UK member, the supposed 750 miles offer doesn't apply to me, but if true could apply to somebody close to me

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The offer to me is along the lines of x miles for £100, y miles for £200 and z miles for £300, where z is greater than x + y. However for a single purchase worth £300 split between two currencies, I got x + y, not z. Pathetic, really.
My ATM card and the M&S service are no-brainers.