Delegates at the conference were warned that inspectors could seek details for journeys made within the past 12 months so it is vital that fleets keep full records.
Ernst & Young tax director Alastair Kendrick said: 'There is a revenue purge in some industries and the Inland Revenue may want details of the postcode drivers went from to the postcode of their destination.
'It is no good just keeping records that say, for example, the driver travelled from London to Leicester. You could be held a hostage to fortune if you do not keep adequate records. Seven-figure settlements are now being sought by the Revenue.'
Kendrick was speaking about the fleet implications of this year's Budget which he said was typical from a Government 18 months away from the election. He also warned companies who run employee car ownership schemes which use the approved mileage scheme to register them with the Inland Revenue and seek full approval.
'It is important to make sure you take steps and take professional advice,' he urged delegates. 'The risk can be significant.'
Paul Jackson, managing director of The Miles Consultancy, told delegates that software systems were available that help fleets gather the right data. Kendrick also welcomed changes to van taxation, saying it was good news for the industry.
Under the current rules, the benefit charge payable for a van available to an employee for private use is £500 (or £350 for a van that is four or more years old at the end of the tax year), a law that has been in place and unchanged since 1993. The charge also includes any private fuel provided.
From April 6, 2005 employees who have to take their van home and are not allowed other private use will not have to pay any benefit tax charge.
From April 6, 2007 the discount for older vans will be removed and the scale charge for unrestricted private use will increase to £3,000.