Yes yes there is an obvious answer to the question but the specific phenomenon of all the big Christmas hits (and Andy Williams) getting back into the Top 40 still bears closer examination. For instance, why is Mariah Carey’s “All I Want For Christmas” the most successful of these re-entries?

The answer lies in the murky world of the Christmas compilation. As anyone who’s ever bought a Xmo CD knows, the Christmas comp is a frustrating beast because it works like a fantasy football team: you don’t have enough money in your budget to get all the big stars so you pad out the disc with the musical equivalent of Sunderland’s second-choice right-back. (or “A Spaceman Came Travelling” as it’s known in the Christmas trade). So inevitably some songs the festive punter expects to find are lacking – and this is where the new download chart comes in.

A quick test of the theory: let’s look at the best-selling Wobs CD on Amazon. Band Aid, Slade, Wizzard….all there. But – NO MARIAH. Hence the disappointed buyers head for itunes to round off their Christmas collection and here we all are!