In November 2008, the Department of Transport published a study into the likely impact of reducing the frequency of MOT tests.
It found that a move from the current MOT frequency regime of testing new cars after three years and annually thereafter (3-1-1) would increase the number of unroadworthy vehicles on the road and risked a significant increase in the number of additional road deaths and serious injuries every year. 
The DfT study found that moving to a 4‐1‐1 system (testing new cars at four rather than three years and maintaining annual tests thereafter) would result in 5 additional fatal accidents every year, and over 2,000 injuries, of which 338 would be serious.
Under the current system, a significant number of vehicles fail their MOT – for example, 285236 MOT test failures were recorded between August 2012 and August 2013.
In 2013-14 – the most common failures were Lighting and Signalling (18.7%), Brakes (10.2%), Tyres (7.7%) and Suspension (12.5%).
Whilst it can be argued that technology is continually improving the safety of vehicles, components that require regular maintenance and replacement will always remain.
If a motorist is not already using other means (servicing, or their own checks) to pick up defects prior to MOT, it is likely that these defects if not detected at a 3 year MOT will still be present at year 4 (which in itself already has a 24.9% initial failure rate) as such the compound failure rate could be as much as 40%.
During the period between year 3 to first MOT at year 4, this would mean a subsequent increase of unroadworthy vehicles on the road and the defects that are on vehicle would be there for a longer period of time.
The MOT test is conducted to a minimum standard (a failure only ensues if the standard reaches the absolute minimum) meaning that on average 40% of vehicles on the road do not reach the required standard and 20% of three year old vehicles also do not.
Half of new cars are purchased and operated for their first three years by company car fleets – and so typically accumulate a far higher annual mileage than the average privately owned car, even more so the car-derived vans that fall under this category - as current MOT failure rates demonstrate, by their third anniversary, it is entirely probable these vehicles will be exhibiting issues that significantly compromise their roadworthiness.
If a car’s annual mileage is 25,000 that would mean a vehicle could have covered 100,000 miles before its first legal inspection – combined with the recent trend towards increasing service intervals to 20,000 and 24 months, a vehicle could have been inspected just once at a garage in the first 48 months.
The number of road casualties would therefore inevitably increase if there were to be an increase in the number of defective cars on our roads.
As a result of the DfT study in 2008, Transport Ministers ruled out pursuing the original policy. The then Road Safety Minister, Jim Fitzpatrick, told the House of Commons:
“Our analysis suggests that a significant number of additional road traffic accidents would be likely if MOT test frequency was reduced. This is primarily because the annual MOT failure rate is already high—around 35 per cent.—and if we were to reduce test frequency there is a very real risk that the number of unroadworthy cars would increase significantly. In turn, the number of road casualties would inevitably increase. Clearly any significant increase in road traffic accidents or in the number of road casualties would be a wholly unacceptable outcome; and, for that reason, our view is that the MOT test frequency should remain unchanged.
At the time of the 2008 report, the decision to maintain existing MOT frequency was strongly supported by the Conservative Party’s transport frontbench team. Shadow Road Safety Minister, Robert Goodwill, now a Government whip, said:
“This botched policy idea should never have seen the light of day. If it had been given the green light we would have faced a situation where there were thousands of dangerous cars on our streets putting people's lives at risk. This is yet another one of Gordon Brown's big flagship policies that has been consigned to the dustbin of history.”
The ‘Transport Research Laboratory’ Study
The issue of MOT frequency was also looked at by the Transport Research Laboratory (TRL) in 2011 - using a different methodology to the 2008 study it estimated a lower impact on road casualties. However, it clearly states:
“The larger the time gap between MOT testing intervals, the larger the predicted number of additional accidents and casualties which may be attributed to vehicle defect contributory factors.”
Some have argued that the TRL study’s understates the likely impact on road casualties as its estimates are based only on increased MOT failure rates and do not reflect the fact that more defects are likely to accompany each failure - in an interview with MOT Testing Magazine, the study’s author, Richard Cuerdon, accepted that his report was “…likely to underestimate the accident outcomes.”
Existing Failure Rates
What is more, the government agency that regulates MOT testing and vehicle safety - the Vehicle and Operator Services Agency (VOSA) - found that more than 800,000 of the cars that failed in a year are described as “dangerous to drive” ‐ that’s 15,000 “dangerous” cars spotted every week.
One in five cars and vans fail the MOT at first test (after three years) – it is estimated that if the first test was at four years rather than three, the fail rate would double to between 36% and 47%.
It is also clear that the MOT failure rate has been increasing in recent years – from 33.5% in 2004/05 to 41% in 2009/10, with vehicle owners cutting back on making necessary repairs through the year a likely explanation.
 DfT, ‘MOT Scheme Evidence base’, 2008
 DfT, ‘MOT Scheme Evidence base’, 2008
 VOSA Effectiveness Report 2013/14
 House of Commons, 8 Dec 2008, col 42WS
 Daily Telegraph, 12th December, 2008
 Effect of vehicle defects in road accidents, TRL, 2011
 MOT Testing Aug-Oct 2011, Issue no. 70
 VOSA, D-Box statistics 2009/10