The boss of a troubled railway company has resigned after months of delays, cancellations and controversy.

Charles Horton has stepped down as the chief executive of Govia Thameslink Railway (GTR), which operates Thameslink and Southern Rail services in Brighton and Sussex.

In a letter to staff, he said the company has gone through “very challenging” times in recent weeks.

Indeed, he admitted that during the furore over timetable changes, he himself was caught up in the delays on his way to work.

Mr Horton said: "I recognise that passengers have been hugely frustrated at the significant disruption caused by the introduction of new timetables. It is the right time to hand leadership of GTR to a new pair of hands.

"I am immensely proud of my team and I would like to thank my 7,000 colleagues at GTR for all their hard work over the past four years."

Services on GTR's Southern and Northern franchises have suffered huge delays since a new timetable was introduced last month.

In his letter to staff, Mr Horton said: "In my view, this was an industry-wide failure of the timetabling process. But with leadership comes responsibility and so I feel it is only right that I step down.

"Before my departure in a few weeks' time, I will continue to work with my colleagues to ensure a smooth handover as we work to put our railway back on track and give our passengers a reliable service once again.”

He added that the changes that GTR are making will be “recognised as a turning point” for services “after years of under-investment”.

But campaigners from the Association of British Commuters say Mr Horton has presided over a period of "absolute chaos".

Founder member Emily Yates said: "It is unbelievable that he hadn't resigned before now.

"But the real resignation we need is Chris Grayling, and we will continue to push for that."

She said the government's Transport Secretary has allowed GTR to breach its franchise, and buy-out of its liabilities during this period, and says Chris Grayling must ultimately take responsibility.

GTR has a parent company called Go Ahead, and its chief executive David Brown said that bosses are “committed” to addressing the problems for the beleaguered firms.

Mr Brown said: “I would like to thank Charles for his hard work with Govia for the past 15 years.

“Under often challenging conditions, he has built a team to deliver the largest railway change programme for decades, on a franchise that is not only the UK's biggest, but which has also has seen the highest passenger growth.

"We are committed to working with the Department for Transport and Network Rail to address recent problems and to deliver a reliable, punctual service for passengers."