We have a BV 7, which we bought 3 years ago. Two days ago we were listening to the radio on it for several hours.

We are still seeing the ghost of the vertical strip from the radio image down the centre of the screen, plus the text in the top right giving the radio program we were listening to.

Is anyone aware of screen burn / retention with BV 7s, and if there is any solution to it.

Try switching it to the analogue tuner, and making sure the aerial is un-plugged so it's displaying snow/white noise, and leave it for several hours. Then switch it off and leave it for a few hours. I've seen screen burn on LCD displays a few times, and usually the white noise will be enough to do it...