The survey, carried out across 38 sites in southeast England by the Transport Research Laboratory (TRL) on behalf of the Department for Transport, showed 1.2% of car drivers using a hand-held phone as they drove. This compared with a pre-ban figure of 1.6% in 2003.

Mobile phone use was at its highest on motorways, and drivers of vans and lorries were more likely to defy the ban than car drivers. Using a hands-free set while driving is the legal way to make calls but the survey found a relatively small increase in the number of people phoning hands free: 1.9% in 2004 from 1.7% in 2003.

Sunday Times Driving carried out its own survey on Hammersmith Broadway, west London, last week, which showed the problem is even worse in metropolitan areas than the picture given by the official survey. Counting 100 cars in mid-morning we found 16 drivers using hand-held phones. We also spotted 15 out of 40 van drivers on the phone.

Drivers defying the ban could face heavier penalties in future. The Road Safety Bill includes measures to increases the fine to £60 plus three points.