Workers at a security company in Sussex are threatening legal and industrial action over plans to install "Big Brother" style tracking devices in their vans.

The Amalgamated Engineering and Electrical Union (AEEU) is threatening court proceedings against ADT Fire and Security unless the row is resolved.

The union says the company, whose engineers fit alarms, is spending £1 million installing satellite tracking devices in its van fleet.

The equipment can track the movements of 1,300 engineers at 32 depots across the country, including one in North Street, Portslade.

Workers there are allowed to use the vehicles in the evenings and at weekends. But they fear the company will use the devices to spy on them.

Gary Pitts, AEUU shop steward for Brighton and Portsmouth, said: "The devices have been trialled at other branches in the country and the stories we are hearing are horrendous.

"People are handing in their notice and suffering from stress. Engineers have been called up and asked why they took a particular route to a call.

"ADT is showing no trust in its engineers. They will be able to monitor what we are doing in our private time and we won't be able to go anywhere without ADT knowing about it."

Union members will be balloted tomorrow over industrial action.

The union believes the firm could be in breach of the Human Rights Act, the Data Protection Act and employment contracts.

It says if it does not receive a response from the company by the end of today, it will consider applying for a High Court injunction to stop the devices being fitted.

ADT said in a statement: "ADT Fire and Security is discussing with the Amalgamated Engineering and Electrical Union the use of a vehicle asset management system on our service vehicles in order to give customers an enhanced level of service.

"We are unable to make any further comment at this time."