Rail passengers could still face travel disruptions despite the completion of £8.8 billion of engineering works, the head of Network Rail has admitted.

Iain Coucher said he could not guarantee a full-proof service to commuters using the West Coast Main Line and said there would still be ‘teething problems’ when a new timetable with increased trains begins on Sunday.

He pleaded with customers not to judge the rail operator, asked for their patience and promised travelling by train would be much better in the future.

He said: “The infrastructure is ready but we are expecting one or two teething problems. But with an investment of this size we don’t want people to judge us on our efforts on Sunday, judge us later on.

“There is a possibility that there might be one or two issues as the railway beds down but judge us in the years to come.

“We have delivered against all of our targets and we have put in place more robust planning on this upgrade than anything I have ever seen since I came to Network Rail.

“I cannot guarantee nothing will go wrong but we have left no stone unturned and I want to thank our customers for their support as we carried out these works.”

Network Rail was fined a record £14 million when engineering works overran at Rugby last January.

Since then it has faced mounting pressure to complete works on time and passengers have endured delays every weekend and on some weekdays as 1,695 miles of track is replaced.

Mr Coucher said 400 extra staff had been employed to work at night time should problems occur on the railway.

He also refused to be drawn on the recent row with Virgin Trains which lambasted Network Rail over the robustness of the engineering works.

Virgin Trains chief executive Tony Collins claimed passengers could face up to six months of disruptions as Network Rail continued to maintain the railway next year.

Mr Coucher said Virgin Trains was a ‘demanding customer’ but insisted the two firms enjoyed a good relationship.

He said: “Virgin Trains has invested a lot of money so it can run more trains and so it really wants us to deliver a high-performing railway.

“Like all of our customers Virgin Trains is very demanding, but I can assure you we are on good terms.

“I met Tony Collins and other senior people on Monday to review preparations for the new timetable.

“We have a great relationship with Virgin Trains but we know there is so much dependent on the performance of Network Rail.”

Mr Coucher also admitted track capacity will still be a problem at the re-designed New Street Station but he said Network Rail was conducting a study into increasing capacity for trains travelling between Birmingham and London, which will be published next summer.

“New Street is creaking at the seams,” he said. “We decided that even if we couldn’t do anything immediately about the track we had to do something about the concourse.

“We recognise track capacity is a problem and the study will look at increasing capacity between London and Birmingham.”

He also stressed the new timetable should ease some of the problems of overcrowding on station platforms as more trains begin to serve New Street.