A British Transport Police spokesman said: “Officers discovered signalling cables had been cut, but not stolen, near to Wood End Lane.

“A full search of the area was carried out by officers on the ground, while Network Rail staff repaired the damage caused.

“Enquiries are ongoing in the area to find those responsible for the damage which has caused ongoing delays, disruption and inconvenience to passengers and the rail industry.”

Network Rail initially hoped to get the problem fixed by 3pm yesterday but the work has dragged on until today.

A spokesman for Network Rail said: “The extent of the damage, and the resulting extensive repairs, means we are still working to fully reopen the railway.

“Engineers worked throughout the night and remain on site, doing all they can to complete the work.

“It appears the damage was caused by cable thieves and we will work with British Transport Police to trace those responsible. We apologise to passengers for the inconvenience caused.”

Anyone with information about this incident is urged to contact British Transport Police on 0800 40 50 40 or text 61016 quoting incident reference number 30 of 19/03/14.