I asked a couple of years ago
I got a nice letter back from the Digital MP saying "Thank you, we have thought of that, and we have plenty of coverage already."
Even in my garden, which Vodafone says will get 3G, we don't have a reliable signal (it seems that pressure and humidity have to be just right to get a signal). You can forget getting a signal in the house, unless you buy a femto-cell from them (pay to get their sh1t signal, no way!).
But my question is - am I included in the 90% coverage? Don't bother answering - of course they count me in!