As the BBC points out, directory services company 118800 will start indexing mobile phone numbers in the UK from next week.

We're particularly worried about this as you will probably not know whether you're on their list. They get their numbers from a variety of marketing sources, with the service allowing people to find your number on the interet.

The best thing to do is register as ex-directory with the firm according to the Beeb, and this is a simple process (I've already done it) that can be done here: http://www.118800.co.uk/ (currently unavailable).