I've got the 17" version of this Wharfedale TV (LCD1710AF), and get a similar problem when it's connected to my DVD player via SCART, and also with the laptop on the VGA input, Raspberry Pi on the phono inputs, and sometimes even just when viewing TV programmes via the internal DVB tuner, and it would happen within about 5 seconds of switching the TV on. I say similar problem because it doesn't actually go onto standby, but the backlight in the screen shuts itself off, the power LED stays green (i.e. 'on') and if you look very carefully at the screen from the right angle you can still just see a feint TV picture. I was able to solve the problem temporarily by just taking the back cover off, prodding a few of the ribbon cables that link the PCBs together and then reassembling it. This lasted a few months but then it started happening again, albeit less frequently. Touch wood it hasn't happened for some time now, but if the problem comes back it's going in a skip and I'll buy something decent.
It really is a cheap and nasty TV and I wouldn't recommend it to anyone.