Button presses are allowed, holding something is not

However if you crash whilst pressing a button, be it the climate panel/radio/ipod/sunroof etc, and this distraction is proven to be a factor then you can expect a careless/due care charge...
As ever though, the media have done a wonderful job of sensationalising an issue... in both the Sun and Daily fail, they ran pictures of people in vehicles doing various hand held things with the suggestion that they were all travelling at 60-70 mph.
Of the six pictures shown, two were trucks (size indeterminate due to cropping, but both Paccar cabs, so 7.5t or bigger) which shouldn't be travelling at more than 56mph... and two were vans (Iveco Dailys iirc, so probably 3.5t) and therefore speeding.
Point is, doing anything other than driving whilst driving creates a distraction, which influences the reaction times. This is not news. Inattentive or inappropriate behaviour alone are what causes potentially fatal crashes. This is why autonomous cars are the holy grail of automotive development... they won't be distracted by facebook updates of screaming children, or watching telly in the middle lane of the M20.