The rail regulator has imposed its biggest ever fine - £2.4 million - on Network Rail after a ten-month delay to a major new resignalling project in the south of England.

The Office for Rail Regulation (ORR) today said the planning and risk assessment involved in the work at Portsmouth fell “well short of the standard we expect”.

Network Rail had hoped to have the new signalling up and running by the end of January. While 80 per cent of the work has been finished the project will not be completed until October.

The delays have cut the number of services that can get through to Portsmouth Harbour and Portsmouth and Southsea stations.

In a stinging verdict, the rail regulator said: “We have concluded this is a moderately serious breach affecting many passengers.

“Similar future breaches elsewhere on the network would have an even greater impact on passengers and train operators.

“We intend to impose a penalty to provide a strong incentive to Network Rail to help ensure it conducts robust risk assessments that reflect the potential impact on third parties and puts in place appropriate management and mitigation measures.”