Concern has been raised over community safety after it emerged street lights could be switched on later or turned down at night in a green scheme aiming to slash energy bills.

Officers from Lambeth Council - which is under huge pressure to cut C02 emissions or face hefty fines - are looking at the scheme that would see street lamps dimmed by between 25 and 40 per cent between midnight and 5am.

The £1.4m scheme would save £150,000 a year in energy bills, and help meet the council’s targets for carbon emissions.

But chair of UK Neighbourhood Watch Trust, Roy Rudham, said it would put community safety at risk, encourage crime and increase fear of crime.

He said: "A lot of crime is committed at night and this would have to be seen as encouraging that. There are already parts of the community who are scared to go out at night. A scheme like this would exacerbate that."

A draft report from council officers, leaked to the Streatham Guardian, accepted it would be "difficult to ‘sell’ this proposition to the public".

But it said in a few years time "as the emissions trading regime starts to bite, and public awareness of the Carbon Reduction Commitment (CRC) increases" it may be an easier option to implement.

The council needs to seriously reduce its carbon footprint under the CRC – a mandatory scheme that would see all large organisations charged for their CO2 production - or face heavy financial penalties in the future.

Lib Dem councillor Julian Heather called the proposals "absolutely outrageous", accusing the Labour-run administration of "risking people’s safety from street crime by making our streets darker and more dangerous in a borough that has one of the highest levels of street crime in London".

He said the council needed to look at cutting its CO2 emissions in other ways, such as putting thermostats in the town hall, where currently windows are opened when it gets too hot.

A Labour spokeswoman said the administration had "no plans" to implement the idea, and said it was simply one of a number of options researched by officers.

Councillor Sally Prentice, Lambeth's cabinet member for environment, said: "Labour has invested millions in new street lighting in Lambeth which has made a big difference to resident’s safety and crime is coming down.

"This is an achievement we would never compromise. We do need to balance this with some of the environmental issues we are all facing so all we are doing is starting to look at ways we can keep residents safe and reduce our carbon footprint at the same time – this is what any responsible leadership would do."

Under the CRC, current street light use would cost the council £52,000 in C02 emissions.

Reducing the brightness of the lights by 40 per cent would prevent 621 tons of CO2 emissions.

Another scheme - where lights would be turned on 10 minutes later in the evening and turned off 10 minutes earlier in the morning - could slash £27,658 annually in energy costs.