"Take a look at the screen in a shop, running real TV programmes, first and then make up your mind."

I was passing a bank of such screens in my local 24 hour Tesco late one night last week. Happened that they'd turned the sound off on most of the TVs, except for one that was tuned to a digital radio commercial station.

Just as I passed (and remember, this was Tesco) it blurted out those immortal words: Sainsburys! Try something new today!

Even more curious, its not just the TV section that churns out commercial radio at night. Shelf stackers, for some reason, can only work to loud radio accompaniment. So at night commercial radio plays out loud and clear adverts for leading competitors on speakers throughout the store.

I wonder if any of their head office staff have ever taken a trip round their stores at night to notice how much they try to divert their customers to competitors at off peak times.