A man in his 20s has been arrested on suspicion of causing death by dangerous driving following a crash on the M25, while a second death has now been announced.

The crash took place at around 4am yesterday (Sunday, February 4), when Hertfordshire Constabulary were in pursuit of a van between Watford and St Albans, which then crashed with three other vehicles.

Following the collision, Hertfordshire police confirmed that a woman had sadly passed away, and that the incident had been referred to the Independent Office for Police Conduct (IOPC).

Herts Advertiser: Two police pursuits preceded the crash.Two police pursuits preceded the crash. (Image: UKNIP)

Officers have now confirmed that a man has also died, and another male in his 20s has been arrested on suspicion of causing death by dangerous driving.

A spokesperson for Hertfordshire Constabulary said: “Officers were in pursuit of a van before the van was involved in a collision with three other vehicles.

Herts Advertiser: The M25, between St Albans and Watford.The M25, between St Albans and Watford. (Image: Google Maps)

“No police vehicles were involved in the collision and the pursuit had been stood down prior to the collision.

“A woman has sadly passed away and her family are being supported by specially trained officers.

Herts Advertiser: A man and a woman have been confirmed dead following the crash.A man and a woman have been confirmed dead following the crash. (Image: UKNIP)

“As a matter of course, the incident has been referred to the Independent Office for Police Conduct.”

The spokesperson later added: "We can now confirm that a man also sadly died in the collision.

"His family are being supported by specially trained officers.

"A man in his 20s has been arrested on suspicion of causing death by dangerous driving."

An IOPC spokesperson commented: “We are investigating police actions prior to a fatal road traffic collision on the M25.

"We understand that at around 4am on Sunday (February 4), Hertfordshire Constabulary were in pursuit of a van before the van was involved in a collision.

"The incident, involving three other vehicles, was between Watford and St Albans.

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"No police vehicles were involved in the collision and the pursuit had been stood down prior to the collision.

"We sent our investigators to the scene and to the post incident procedure to begin the process of gathering information.

"Our investigation is in the very early stages."