A third of a million more vehicles have been taxed this year following the use of automatic fines for those failing to update tax discs, the government says.
Many motorists awoke to fines on Monday under the new rules
The rise will help cut the number of motorists who fail to buy insurance and make it easier to track criminals, the Department of Transport said.
It has also encouraged more drivers to get an MOT on their vehicles.
Ministers say their tougher line has made the roads safer and the system fairer for law-abiding motorists.
Thousands of drivers who failed to renew their tax discs faced receiving an £80 penalty in the post after the new enforcement scheme was introduced in March.
The Driver and Vehicle Licensing Agency (DVLA) last month sent 97,000 penalties to UK motorists whose discs expired at the end of December.
Until 15 March, a motorist only faced a fine if their untaxed vehicle was spotted on the road, for example by a police officer.
Car owners who fail to notify the DVLA when they sell their vehicle can also now be fined.
Owners who have sent their cars to be scrapped or store them off a public road without informing the DVLA can also be similarly targeted.
Vehicles without a valid tax disc also stand a greater risk of being clamped under the new rules.
RAC Foundation boss Edmund King told BBC News Online: "We approve of the principle of automatic fines as long as there are safeguards for people such as the elderly, who may be confused by the changes, or motorists who are on holiday and unable to update their discs."
Road Safety Minister David Jamieson has previously said the vast majority of law-abiding motorists would remain unaffected by the changes.
"They've always ensured their vehicles were licensed and renewed on time," he added.