More than 27,000 street lights in Norfolk are to be switched off after midnight as the county council looks to save money.

The idea to turn off lights between midnight and 5am was mooted more than a year ago and has already happened in some towns and villages – including Wymondham – with few rumblings of discontent. But critics argue that turning off lights in market towns with low crime rates cannot be compared with turning them out in the city.

Thousands of families in the north of Norwich are receiving letters giving them one last chance to make the case for keeping the lights on in their streets. The council is seeking to turn off up to 5,900 lights in the city.

Officials hope the savings will save �167,000 countywide and reduce carbon emissions.

John Birchall, spokesman for Norfolk County Council, said: 'We have worked with local city and county councillors and the police to refine the list of streets that appear suitable for part-night lighting.

'Letters will be going out to residents in the north of the city, including streets considered suitable in Mile Cross, most of Catton Grove and part of Sewell electoral division west of Sprowston Road.

'Only people living in streets where part-night lighting is proposed will receive a letter. Those who do then have a chance to put forward reasons why their street should be exempt.'

The county council, which is having to make �155m in savings over the next three years, says some streets will be spared if families can make a case for exemptions to be applied.

It is likely that the first switch-off of lights after midnight in Norwich will happen in March. But 1,000 lights within the inner ring road will not now be part of the measure, after talks with interested parties showed there were few street lights suitable for switching off in that area.

People in the north of the city are the first to receive their letters; those in the southern, western and eastern parts will get theirs later this year.

Steve Morphew, leader of Norwich City Council, still believes the county council has got it wrong. He said people could not compare turning out lights in Norfolk's market towns with doing the same in such an urban area.

Mr Morphew said: 'We have to keep the pressure up, because this proposal is just madness. A couple of weeks ago we had people sliding around on icy streets. Imagine how much worse that would be in the pitch black.

'It's not creating much in the way of savings and could lead to extra costs elsewhere. We've spent years trying to design out places where people can conceal themselves so there are fewer places for people who want to create mischief.'

Norfolk police say there has been no noticeable surge in crime in other places where lights have gone out after midnight. Safer neighbourhood teams have been consulted before decisions have been made about where lights will go out. Supt Gavin Tempest said: 'Areas which have experienced anti-social behaviour or are monitored by CCTV are not included in this, and it only applies in areas which do not suffer from crime.'