The Unite union is warning the M25 could be turned into the "highway to hell" by industrial action.

Connect Plus Services is a a joint venture company that provides maintenance and undertakes emergency responses on the motorway, but its workers are currently being balloted on whether to take industrial action over pay.

A spokesman for Unite said: "Strike action will inevitably result in an increase in traffic jams on the M25, with any delays being for a prolonged period."

The firm's 150-plus workers have rejected a pay offer of 5.3%, stating that once inflation was taken into account that amounted to a pay cut.

The ballot for industrial action opens on Monday next week and closes on Friday, March 31. If members vote for strike action, stoppages could begin as early as mid-April.

The Unite general secretary Sharon Graham said: “Our members perform an essential role in keeping the M25 moving. It is completely unacceptable that Connect Plus is trying to force through a real terms pay cut.

“The company needs to realise its actions are unreasonable and return to the negotiating table with a vastly improved pay offer.

“Unite is now entirely focused on the jobs, pay and conditions of its members and the workers at Connect Plus Services will receive the union’s complete support.”

The workers undertake general maintenance duties to ensure the M25 operates smoothly. They install and maintain traffic management systems during repair work and liaise closely with National Highways traffic officers.

They are also responsible for all elements of emergency repair work on the motorway, including at accident sites, barrier repairs and dealing with floods and melting tarmac. The workers are also responsible for the winter maintenance contract including gritting.

Most of the workers get £13 an hour yet many require an HGV licence in order to use the heavy plant vehicles needed for their roles.

Unite regional officer Malcolm Bonnett said: “Strike action will inevitably cause severe delays and disruption on the M25 and turn it into a highway to hell."

Connect Plus Services is a joint venture company operated by a partnership of Balfour Beatty, Egis and Aitkin.

A spokesman said: "We remain committed to working closely with Unite the Union to reach an appropriate outcome.

"However, as these discussions remain ongoing, it would be inappropriate to comment further at this time."