The move follows a ballot of workers, which closed a week ago, to reject a new revised pay deal.

The offer was worth an average increase of 4.2% and two extra days off for staff with more than ten years service.

But Unison said its members had voted three to one against the deal and had now resumed a work to rule.

Response times increase

The action means ambulance crews are refusing to record response times to call-outs and will not be providing cover for neighbouring stations.

The Sussex Ambulance NHS Trust said unions had gone back on an assurance that action would not begin again until talks had been reconvened.

A spokesman said that the move would inevitably increase response times - and that the management was angry and disappointed at the decision.

But Unison says the action was called because of frustration that management seemed unwilling to meet.

Fresh talks have been arranged between the two sides for early next week.