They have been appearing on traffic lights all over Norwich, leaving motorists scratching their heads over whether they are cameras, sensors or solar panels.

The little grey boxes have been installed on sets of lights in the city, leading drivers wondering just what they are.

But highways bosses at Norfolk County Council have now solved the mystery.

They have revealed that the boxes are part of a £750,000 scheme to get traffic lights on-line - at a time when the council is having to make nearly £53m of savings and cuts.

The council operates what is called an Urban Traffic Control System, a series of sensors which helps it monitor, control and co-ordinate traffic signal junctions and pedestrian crossings in Norwich, King's Lynn and Great Yarmouth.

Until now, the network has been connected by 148 lines and private data circuits leased from BT.

However, a county council spokesman explained: 'In 2004, BT announced they would no longer be providing additional lines and would be discontinuing support for this type of line from 2018.

'The latest digital technology is not compatible with the existing circuits, and therefore Norfolk County Council needed to investigate cost effective options to refresh the underlying network and to provide a service that caters for future innovation in transport network services for the county.'

In January, the council awarded a contract, worth up to £30m over 12 years, to global technical services provider Imtech to handle the council's traffic signals maintenance.

As part of that contract, which was agreed after a tendering process, £753,000 is being spent to replace the BT lines with a wireless network. The council says that will save £140,000 a year and keep the network connected.

A council spokesman said: 'Further savings will be made on completion of the project when old equipment can be decommissioned.

'Traffic signals are being connected via antennae mounted on top of existing traffic signal poles with some additional repeaters attached to lamp columns.'

Norfolk County Council, which agreed £40m of savings in 2015/16 is currently consulting on £12.9m of possible savings and cuts, including reducing highway maintenance, slashing funding for arts and cutting library staffing.

• Do you have a story about a local council? Call reporter Dan Grimmer on 01603 772375 or email dan.grimmer@archant.co.uk