Two million warning letters have been sent out to motorists since rule changes came into force which mean that vehicles have to be insured unless they are formally declared as being off the road.

The Motor Insurers' Bureau (MIB) said it sends out 60,000 letters a month to people whose vehicle is not recorded on the Motor Insurance Database, to alert them about the consequences of not insuring their vehicle or declaring it off road.

Recipients who fail to comply face a £100 fixed penalty, having their vehicle clamped, seized or destroyed or being subject to a court prosecution and a fine of up to £1,000.

The two millionth warning letter was issued earlier this month. One third of people who have received such correspondence in the last three years have ended up receiving a fixed penalty.

While the majority of people take action to comply with the legal requirements after receiving a letter, as many as 6,000 people are prosecuted each month, the MIB said, highlighting the persistence of uninsured driving in the UK.

Changes were introduced in 2011 which require the registered keeper of a vehicle to have insurance at all times, unless they have declared the vehicle off the road with a statutory off road notification (Sorn) to the DVLA.

Before the changes under the Continuous Insurance Enforcement (CIE) scheme came into effect, someone who owned a vehicle but did not use it could keep it off the road without insurance, but they did not have to formally declare they were doing this.

The scheme was introduced to tackle levels of uninsured driving. Uninsured and untraced drivers kill around 130 people and injure 26,500 every year, as well as pushing up the cost of all drivers' premiums.

The MIB said research shows that uninsured drivers are five times more likely to be involved in road collisions than ordinary drivers and are also more likely to be engaged in other types of criminal activity.

People who drive uninsured could end up having their vehicle seized and possibly crushed as well as the prospect of a £300 penalty, charges for recovering the vehicle and points on their driving licence or a driving ban.

But the MIB also said that for some people who are keeping their vehicle off road, it simply has not occurred to them that they need to have insurance.

It quoted the recipient of one insurance advisory letter named Craig Coburn, who keeps his motorcycle parked in the garden in preparation for passing his test. Mr Coburn did not realise he needed to keep the vehicle insured or declare it off road if he was not using it.

He said: "I was quite surprised to get the letter but grateful for the warning and took out insurance straight away. I think there is a lack of understanding out there about what the law is and think it's important to raise awareness."

The MIB said that other reasons given by people for not insuring their vehicle or declaring it Sorn have included: "I only use my tractor to cross 10ft of tarmac," and: "I've got a motorbike that I only ride in the summer."

Ashton West, chief executive of the MIB, which acts as a safety net for victims of accidents involving uninsured and untraced drivers, said the CIE scheme has contributed to a fall in claims being made to it by such victims.

He said: "This reduces the cost paid by the honest motorist in insurance premiums, but more importantly means that fewer people are being injured and killed by uninsured drivers."

Motorists can check whether their vehicle appears on the Motor Insurance Database at www.askMID.com.

The MIB said people should also check that their vehicle and personal details are correct on their policy documents. If someone is no longer the registered keeper of a vehicle, they should notify the DVLA.

Transport Minister Robert Goodwill said: "We introduced tough new laws in 2011 to tackle uninsured drivers who are not only a danger on our roads but also increase premiums for honest motorists.

"I am really pleased to see that Continuous Insurance Enforcement is working well and urge motorists to make sure their vehicle is insured at all times unless they have told DVLA that it is off the road."