Check with your Solicitor. I know you have been there for a long time but the public adoption (or otherwise) of the road should have been clear at the time.
It's not just the street lights. A private road including the surface of the road, the footpaths and the sewers underneath are all maintainable by the frontagers. Do check with your Water Company, they should advise you if they think the sewers are adopted. It's got the look of a mistake somewhere.