Union bosses are threatening "gridlock" on the M25 next month if workers vote for strike action in a dispute over pay.

The union Unite is balloting members employed by Connect Plus Services.

It is a consortium which includes Balfour Beatty, Egis Road Operation UK and Edge Orbital Holdings Ltd. It holds a 30-year contract to provide road maintenance on the London orbital road and the Dartford Crossing.

Among the safety critical roles the consortium carries out is gritting the motorway during cold weather.

If strike action is agreed, the industrial action could start at the end of January.

Unite says the row centre on a pay deal it had agreed with Connect Plus Services but which Balfour Beatty has now "reneged" on.

It claims a negotiated two-year pay deal, beginning in 2020, worth 6.25% and a £500 bonus for each worker was agreed with local management.

However, it says, the pay deal was vetoed by senior management at Balfour Beatty, who ruled it was above what other workers in the company would receive and that Connect Plus management did not have the authority to negotiate on pay.

The strike ballot will run from Friday, December 27 to Monday January 13.

Unite regional officer Malcolm Bonnett said: “Our members are angry and frustrated that a pay deal that has been correctly negotiated and agreed in good faith has been vetoed.

“If strike action does take place then it will inevitably cause chaos for drivers using the M25 and could potentially result in gridlock affecting London and the south east of England.

'If strike action does take place then it will inevitably cause chaos for drivers using the M25.' - Unite's Malcolm Bonnett

“This dispute is entirely of Balfour Beatty’s making and they could easily resolve this dispute by honouring the pay deal which was previously agreed.”

A spokesperson for Connect Plus Services, said: “We can confirm that we have received notice from Unite as to their intent to hold a ballot for their Connect Plus Service members to consider industrial action.

"We continue to work with Unite with both sides fully committed to reaching an agreement. As discussions are ongoing, it would be inappropriate to comment further at this time.”

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