Next month's ending of the need to display a car tax disc could lead to tax evasion costing the economy £167 million a year, according to the RAC.
It said it feared that the number of tax-dodgers could equal the number who try to avoid paying motor insurance.
RAC chief engineer David Bizley said: "We could be looking at around £167 million of lost revenues to the Treasury, far exceeding the £10 million that will be saved by no longer having to print tax discs and post them to vehicle owners."
From October 1, motorists will no longer need to display a tax disc on their vehicle windscreen. They will still need to pay their vehicle excise duty car tax, with records being monitored electronically.
An RAC survey of more than 2,000 drivers showed that 36% were unaware of the scrapping of the paper disc, while 47% did not know when the change was due to take effect.
The poll also showed that 63% feared there would be a rise in the number of untaxed cars on the road, while 44% reckoned the change would actually encourage people to break the law.
From October 1 vehicle tax will no longer be transferred when a vehicle is sold, with buyers of used vehicles having to renew the tax when they make a purchase.
Mr Bizley said: "There is clearly concern among motorists over the issue of enforcement. Most of the changes make sense and will benefit the motorist, but too many motorists are unaware of the detail.
"The big question has to be whether enforcement using only cameras and automatic number plate recognition will be sufficiently effective."
Paper car tax discs are being abolished from October 1, 2014.
Some answers to common questions being asked:
Q. Will I be fined if I display a tax disc after October 1, 2014?
A. No. There will be no legal requirement to display a disc from October 1 onwards but if your disc is still in date, there is no need to remove it. If you sell your car, you need to inform the DVLA immediately as otherwise you could face a fine. The DVLA will cancel your tax disc and refund any duty remaining.
Q.How will I know if a vehicle is taxed?
A.Any person may check the tax status of any vehicle by using DVLA's Vehicle Enquiry System. The vehicle enquiry system can be accessed by visiting gov.uk.
Q. How do I register my car for tax?
A. If your vehicle is taxed then you won't need to do anything at all until your tax is due to expire. You will still receive a V11 reminder from the DVLA and you can still pay for your disc at Post Office branches by cash, cheque, debit or credit card, or online at www.gov.uk/tax-disc. The only difference is you won't be issued with a disc.
Q. What do I need to be able to tax my vehicle?
A. Your vehicle must be insured and either have a valid MOT certificate or be exempt from requiring one. If you're renewing at the Post Office, you will only need your V11 tax reminder form or your V5C registration document (log book) to be able to renew your tax.
Q. I've just bought a car, what do I do?
A. Your new car will need to be taxed before you can drive it. You can do this at the Post Office with either the V5C registration document, or the V5C part 2 New Keepers Supplement. Further information about registering a newly purchased vehicle is also available at www.gov.uk/vehicle-registration.
Q.The tax disc is part of our motoring heritage. Why destroy it now?
A.This is part of the Government's plan to Modernise Motoring Services.
In December 2012 the Department for Transport (DfT) launched a public consultation "Motoring Services Strategy".
The majority of respondents agreed for the paper tax disc to be abolished. Displaying a paper tax disc is now considered an outdated way to identify untaxed vehicles as technology is available.
DVLA VIDEO:Vehicle tax changes explained:
