Oddly, you can use Amex at Waitrose and those John Lewis with a Waitrose attached (Waitrose Food and Home they are called, eg the one at Canary Wharf). It's all very strange! If you were planning on making a mega purchase (TV etc) at Peter Jones or JL Oxford Street, you may prefer to do it at Canary Wharf and use your Amex.

(Of course, now that Tesco has improved its mileage awards, the difference with Amex is a lot smaller going forward.)