The parents of two young sisters who were killed in a horrific motorway crash on Britain's M25 early today also lost a son in a road accident eight years ago, it has emerged.

Relatives of victims of the Potters Bar rail crash tonight attended a special community church service.

Grieving relatives are at Potter’s Bar railway station as Transport Secretary Stephen Byers disclosed that vandalism and individual error were still among the possible causes of Friday’s rail disaster.

Rail crash investigators are today trying to establish what caused nuts to come loose on a points system near Potters Bar station, blamed for the train derailment which claimed seven lives.

A points failure tonight emerged as the likely cause of the Potters Bar rail disaster which claimed the lives of seven people and injured dozens more.

Seven people were killed and five more suffered critical injuries when another disaster struck the British railway network.

Latest reports suggest there are now five people dead after a train derailed outside London this afternoon.

Police feared that death had returned to the railways today after a three-carriage passenger train derailed, apparently smashing into a railway bridge north of London.