A construction firm is to be investigated after a sewer in Radlett was blocked by concrete.

Motorists have been warned that the A5183 Watling Street in Radlett will be fully closed from A411 Elstree Crossroads North to the A414 North Orbital Road from 8pm tonight (Thursday).

Thames Water has been dealing with a blocked sewer near Radlett Station under an emergency response permit since February 19.

The sewer has been completely blocked by concrete, causing sewage to back up and a full replacement is needed where the concrete is causing an obstruction.

Cllr Terry Douris, Herts county council’s cabinet member for highways said: “We are extremely frustrated this situation has arisen due to what appears to be someone’s irresponsible actions and residents affected by this disruption have our sympathy.

“Due to the nature of these works council taxpayers will not be footing the bill.”

He added: “We are doing everything in our powers to limit the disruption caused during this time. We are insisting that works be carried out 24/7 to minimise the duration of the closure with noisy works kept to a minimum during the night time periods.”

Thames Water operations manager Mark Grimshaw said: “Normally blockages are caused by fat, oil and grease building up in the sewer but unfortunately in this case it’s concrete, so we can’t just jet it through.

“It’s in there and it’s set to the pipe, so unfortunately it means we need to remove the pipe and replace it with a new one.

“This is very frustrating and not the first time damage has been caused by private contractors pouring concrete into our sewers.

“Our main priority is to fix the problem and restore normal service as soon as possible, and then reclaim the costs from whoever is responsible.”

A full road closure will be in place until 8pm Saturday March 8.

The road is likely to be closed from A411 Elstree Crossroads North to the A414 North Orbital Road. However local access will be maintained to traffic as the excavation will only fall within a small section of the road.

A fully signed diversion will be in place via the A414 North Orbital Road roundabout, A405 North Orbital Road, A405 Kingsway, A41 North Western Avenue and A41 Colney Way.