Safety has become one of the greatest car marketing tools. I know, I fell for it. When I was buying a car to coincide with the arrival of my baby daughter, the EuroNCAP website first port of call when assembling a shortlist.

I needed something small but built like Fort Knox. At the time, only a few superminis possessed five-star NCAP ratings, a fact which helped to distinguish the few that did. There were plenty of other factors behind my eventual purchase of a Mercedes A-Class, but the fact it possessed five stars certainly played a big part in selling it to me..

But now I fear that EuroNCAP is in danger of losing its meaning. The big news from yesterday's release of results is the fact that Toyota's Urban Cruiser has been awarded a lowly three-star rating. That was certainly a shock - not least for the company's own safety engineers.

But behind the big headline the more telling story is that nine out of the 11 cars tested earned the maximum five-star rating.

Indeed, as Toyota has discovered, it has become more of a story when a car fails to collect one than when it wins the top accolade. NCAP seems to be a victim of its own success, with entire market segments now consisting of wall-to-wall five-star ratings.

Of course that's good - NCAP has driven up standards and even its many detractors (including some in the motor industry) would be hard pressed to argue that an increasing emphasis on impact protection is a bad thing. But it also means the test is losing the ability to help buyers choose between cars.

Behind the numbers, NCAP recently revised the test to increase emphasis on pedestrian protection and to give a breakdown of percentage scores in different areas. But that's the sort of data that requires buyers to put in some serious online spadework to properly compare potential purchases.

So here's my suggestion: NCAP should introduce a super-stringent sixth star. That would sidestep the problem of 'grade deflation' that comes by making five stars harder to earn, and thus preventing fair comparison of cars with the same score tested at different times.

Equally usefully, it would also help illustrate the rate at which modern cars are getting safer.