The National Cyber Security Centre and the National Crime Agency have been called in to help Transport for London deal with a cyber attack, less than two weeks before the BBC launches a drama which depicts chaos on the railways after computer systems have been penetrated.

Transport for London says its transport services have not been affected, and it believes details of customers held on systems like the Oystercard database are safe.

This morning the TfL website says: ‘We are currently dealing with an ongoing cyber security incident. At present, there is no evidence that any customer data has been compromised and there has been no impact on TfL services.

‘The security of our systems and customer data is very important to us, and we have taken immediate action to prevent any further access to our systems.

‘We are working closely with the relevant government agencies to respond to the incident.

‘We will update you further when the incident has been resolved.’

Earlier, TfL’s chief technology officer Shashi Verma had said:‘ We have introduced a number of measures to our internal systems to deal with an ongoing cyber security incident. The security of our systems and customer data is very important to us and we will continue to assess the situation throughout and after the incident.

‘Although we’ll need to complete our full assessment, at present, there is currently no evidence that any customer data has been compromised. There is currently no impact to TfL services and we are working closely with the National Crime Agency and the National Cyber Security Centre to respond to the incident.’

The drama Night Sleeper tells the story of an overnight train from Glasgow to London which is sabotaged by hackers and becomes out of control. The series starts on BBC1 on 15 September.