UK rail leaders have apologised to MPs for the recent timetable overhaul that has caused major disruption on the country’s railway network over the past weeks.

Bosses from infrastructure manager Network Rail and train companies Govia Thameslink Railway (GTR) and Northern appeared before the Commons Transport Select Committee on Monday in a bid to explain why the new schedule shake-up has led to hundreds of service cancellations and delays since it came into effect on 20 May.

Routes covered by GTR and Northern were the most affected by the timetable changes, which forced both companies to introduce temporary timetables at the beginning of June and to remove about 6% of daily services.

Speaking to Parliament members, outgoing GTR chief executive Charles Horton, who offered his resignation last week, cited Network Rail’s “slow pace” in putting the timetable together as the primary cause of the situation. This resulted in driver training and rostering operations being compressed into a shorter time frame than usual.

Horton said: “I’m terribly sad and terribly sorry that it has ended as it has. All the detailed complicated resource planning tasks, which we would normally spread over 12 weeks, we had to complete in three weeks.”

He explained that there is nothing wrong with the plan itself and blamed the delays on its implementation: “Ultimately the result I think for customers is going to be very good, we will see those new journey opportunities opening up, we will see that new capacity, we will see that improvement in the quality of services. The problem we’ve been dealing with is the execution of the timetable has not gone well.”

Hugh Merriman, Conservative MP for Bexhill and Battle, said: “I’m just amazed that there wasn’t a timetable project manager who went round and got your sign-offs, reported to the Department of Transport and various others. I’m just really staggered that that didn’t exist.”

Network Rail heads also faced questioning from MPs, with managing director and system operator Jo Kaye saying she was “deeply sorry” for the shambles and that the time taken to rewrite schedules was longer than expected.

“Everyone was absolutely in a spirit of hugely positive forward momentum to make those changes happen for the benefit of passengers in the round,” she said.

“Clearly with hindsight, you might describe it as ‘over-ambitious’, but at the time we were rightly committed to making those changes.”

Northern managing director David Brown said he was “personally and truly sorry” about the overhaul and that he had asked for the implementation of the scheme to be postponed. However, he claimed “a significant number of other players did not want that to happen”.

Brown’s intervention came the night before Northern staged a 24-hour strike that is set to be repeated on Thursday and Saturday. Members of the Rail, Maritime and Transport union called for a service stoppage in protest of the company’s plans to impose driver-only services.

On Monday night it appeared that the Labour Party is seeking a ‘no confidence’ motion against Transport Secretary Chris Grayling as a consequence of the timetable shambles.