More than 150 police officers have carried out a series of dawn raids in connection with a string of armed robberies.

Three men and a woman were arrested in the swoop, relating to robberies across the South East.

Officers from British Transport Police, Essex Police and the Metropolitan Police, including armed officers, took part in the operation that saw three addresses raided simultaneously at 4am on Thursday.

A 61-year-old man and a 34-year-old woman were arrested in Dagenham, east London, a 35-year-old man in Canning Town, east London, and a 49-year-old man in Canvey Island, Essex.

They have been taken to police stations in Essex and are being interviewed.

One of the armed robberies related to the arrests was the May 2007 raid on security staff delivering cash to Rayleigh station near Southend, Essex. Commuter Adam Mapleson was shot in the chest after he intervened to help the security staff.

Detective Superintendent Michael Field, who is leading the Rayleigh inquiry, said: "The teams entered all three addresses simultaneously at 4am.

"The suspects were immediately arrested and have been taken into custody where they are currently being questioned.

"We have been working closely with Essex Police and the Metropolitan Police on this joint inquiry over many months. Throughout we have been keeping the victims, the security guard who was threatened and Mr Mapleson, updated on the progress that has been made."