The Home Office has doubled fines for drivers and passengers not wearing a seat belt to £60.
It said the previous fine of £30 was not a sufficient enough deterrent, and the new on-the-spot penalty will come into effect from today.
Fines for motorists who deliberately disguise or illegally alter their number plates have also been doubled to £60.
Police fear that the problem is growing as more and more motorists doctor their number plates to avoid detection from speed cameras.
The Institute of Advanced Motorists have welcomed the tougher new penalties, but fear they will be ineffective without proper police enforcement.