Sir Richard runs Virgin Trains
Sir Richard Branson has warned that rail travellers on the West Cost Mainline could face more disruption as the line undergoes an £8.6bn upgrade.
Sir Richard, who owns Virgin Trains, said the line, which links London to Scotland via Manchester, had seen a sharp drop in reliability.
He called on Network Rail to extend the deadline for the work, which is due to be completed by December.
Rail passengers endured severe delays at new year after work overran.
In a letter to the Financial Times, Sir Richard said that since the new year overrun, the number of weekend and weekday closures had risen dramatically.
He said that Network Rail's December deadline was "unrealistic" given the complexity of the project.
"We expect further closure throughout 2008 as Network Rail strives to meets its deadline," the letter said.
The line is due to see an increase in journeys in December, and Sir Richard said he feared that things could get even worse once the new timetable came into effect.
Extending the December deadline would minimise unnecessary disruption to passengers, he added.
The line will be affected by engineering work over the bank holiday weekend.