In January a haulage boss and his mechanic were jailed for a tipper truck crash which killed four people. The brakes on six of the truck's eight wheels weren't working properly. The expert examiner from the Driver and Vehicle Standards Agency said Grittenham Haulage's vehicle would have been taken off the road if it had been stopped in a roadside check. But are there sufficient roadside and on-site checks to detect safety breaches? File on 4 uncovers cases where unsafe vehicles and drivers were allowed to remain on the roads, despite known concerns. So does the current system of regulation and punishment go far enough to deter rogue operators who drive some of the most dangerous vehicles on our roads? Reporter: Jane Deith Producer: David Lewis.