More than 50 firefighters are to 'battle' a blaze and crash in the Dartford Tunnel tonight.

But no-one will be injured in the scenario, which will be staged to test a £34m upgrade to a fire safety system.

The 'full-scale overnight live exercise' will mean both bores of the Dartford tunnel being shut from 10pm to 4am tomorrow - adding about 30 miles onto drivers' journeys.

It will involve firefighters in seven engines working with the police, Red Cross and the ambulance service to create a scenario of a fire in the tunnel.

Kent Fire and Rescue Services spokesman Greg Theophanides said: “Dartford Tunnel plays a vital role in keeping the county’s road network moving.

"However, fires in tunnels can be the most difficult to deal with and pose unique challenges.

“It can be harder for rescue teams to reach the scene, the conditions are confined and it gets incredibly hot and humid.

"This is why we must be able to put our emergency plans into operation effectively.

“The activation of the new fire suppression system will knock the fire back quickly, making it safer for our firefighters and tunnel users.”

The scenario will see a van travelling in lane one suffering a sudden tyre failure.

It will swerve and hit a second vehicle, causing smoke and activating the all-new fire suppression safety system, which was installed as part of a £34 million safety upgrade.

In order for local authorities to carry out this exercise both lanes of the tunnel will be closed, with all traffic diverted to the Blackwall Tunnel.

The Queen Elizabeth II bridge will remain open to southbound traffic.

Chris Brown of Connect Plus, which runs the tunnel, said: “Simulations like this are essential to ensure our readiness to deal swiftly and effectively with any incidents in the tunnels.

"The exercise also gives us the opportunity to ensure that the emergency procedures and equipment perform along with the ability of the organisations taking part to work together in an emergency situation.”

Mr Theophanides added: “Although safety standards in the tunnel are very high, it’s vital that our contingency plans are as robust as possible.

“This innovative training session will allow our firefighters to bring to life possible events that we could be called to deal with and make sure we are all equipped and prepared to deal with it safely and ensure the safety of motorists.”

Highways Agency project manager Paul Harding said: “Safety is a top priority for the Highways Agency and, although we hope an incident like this never happens, we want to make sure that our teams and the emergency services are prepared.

“The tunnel safety systems have been upgraded to ensure that journeys remain safe for the thousands of drivers that use the Dartford Crossing each day.”