During their visit, they found a white pickup truck, believed to be a Volkswagen Caddy, and attempted to speak to the occupants.

One of the officers, a sergeant, was next to the stationary van as it pulled away at high speed, hitting him and knocking him to the ground.

He suffered minor injuries as a result.

Police have released an image of a man they would like to speak to as part of their investigation.

Detective Sergeant Helen Dickson, of the local Watford Crime Unit, said: ‘We have been thoroughly investigating this incident but have now chosen to release this photo.

“We used photo editing software to clarify this image of a man that we would like to track and talk about as part of our investigations.

“We think he has key information that could be very useful to us, so if you know who he is, please contact us as soon as possible.”

Information can be communicated by email to [email protected], online at herts.police.uk/report, via online chat at herts.police.uk/contact or by calling non-urgent number 101.

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