Train companies, such as Virgin's West Coast, have been hiding as many as 54 of their most unpunctual days a year from rail passengers' view - by declaring them "void".
The void days, which do not show up in the performance statistics, were used by BR as a way of compensating season-ticket holders.
But they now mask some of the worst journeys experienced by the travelling public. Companies with few season-ticket holders are declaring voids when passengers are left stranded for hours on broken down trains, or when trains leave hours late.
"It became evident that we were seeing a rather rapid rise in void days," said a spokeswoman for the Shadow Strategic Rail Authority. "There were so many void days that there were instances of major manipulation. We have consulted on a new performance measure which will sort this problem out." But pressure will now come from MPs, including the Liberal Democrat transport spokesman, Norman Baker, for void days to be abolished.
The rail companies have to compensate season-ticket holders for every void day declared but only a tiny proportion of passengers on the worst offending routes hold season tickets.
Less than 4.5 per cent of the passengers on Virgin's three West Coast routes have season tickets. Yet the group had the highest number of void days. In the year ending in March, Virgin's West Coast North West line declared 43 void days, its Scottish route 54 and its West Midlands line 40.
Commuter lines - such as Silverlink Trains' North London Lines, which declared only 11 void days in the year to March - have far more season- ticket holders so declaring void days costs them thousands of pounds in compensation.
North Western Trains, ScotRail and Northern Spirit did not declare any void days during the same period. South West Trains' Main Line declared only 5.5.
A spokeswoman for Virgin, which last year infuriated John Prescott by leaving several Ministers stranded on their way to the Labour party conference, said that most of the void days were due to events outside the company's control.
"Let's call them compensation days and not void days," she said. "They are generally things which are out of our control. Thirty per cent are down to Virgin. About 70 per cent are due to factors other than Virgin, such as collapsed overhead wires. We have to call a void day if passengers on our trains are having a really bad day."Reuse content