Archive pictures from an ITV report on the Moorgate tube crash in February 1975 show the tragic extent of the incident.
Officers search through rubble-strewn carriages at the scene where 43 people lost their lives after the driver failed to stop at the station.
The exact cause of the driver's failure to stop the train was never determined. However, following the incident extra safety measures known as the "Moorgate protection" were introduced, which automatically stop a tube if the brakes are not applied.
A memorial honouring the victims will be unveiled in Finsbury Square this afternoon.