Bruce Williamson, from Rail Future has said that Network Rail is struggling “under tight financial control” and delays due to leaves on the line show that they have had to make “cutbacks”.
A government review, published on Wednesday, revealed that delays caused by falling branches and leaves on the line have increased by two thirds since 2010.
Network Rail’s failure to manage trees by the side of the 20,000-mile network had the “potential to impact as much on safety and performance as on biodiversity”, the review found.
Mr Williamson told talkRADIO’s Mike Graham: “It is very disappointing to put it mildly because it is one of those things that is on-going.
“It is every year because trees are growing and they need to chopped back.
“It looks like on this one, Network Rail have taken their eye off the ball and it has come back to bite them ever so slightly.
“To be fair to Network Rail, they have got a lot to deal with because they are under tight financial control.
“They may have made some cutbacks there and are now paying the price for it.”
Figures released by Network Rail show more than 400 trains hit fallen trees last year.
Rain can make leaves stick to rails, creating a slippery layer which makes it harder for trains to brake and accelerate.
'Tiny baby steps'
Earlier this week, a new independent body was launched to deal with passengers' complaints against rail companies.
The Dispute Resolution Ombudsman has been appointed to act as an independent body to hold train companies to account.
Mr Williamson described the new ombudsman as a "step in the right direction".
“There is a new ombudsman, which is there to handle disputes when you have a complaint about a rail company. The ombudsman would sort it out," he said.
“I think it is a good thing, and a step in the right direction but obviously it is all tiny baby steps.
“We cannot shift this super-tanker of a railway overnight. It is going to take a long time I fear.”