A controversial chemical will continue to be used to kill weeds around Norwich after alternatives, including vinegar, were ruled out following trials.

The city council has long used glyphosate-based weed killers, but concerns have been raised about its impact on human health.

In 2015 the World Health Organisation said it 'probably' caused cancer, although several other organisations did not come to the same conclusion and manufacturer Monsanto says it is safe.

However, the city council last summer asked its contractor Norse to look at alternatives.

A trial was conducted in Earlham Cemetery, with vinegar among the substances tested.

Green city councillor Denise Carlo last night raised the issue at City Hall, questioning how serious the council's commitment to finding an alternative was.

She said vinegar was not recommended as a tool for large-scale weed control.

Kevin Maguire, Labour's cabinet member for safe city environment, said: 'Investigations of alternatives to glyphosate based products have been trialled, not least because the council is continually examining potential efficiency savings in all areas of the joint venture and to meet the council's environmental responsibilities.

'With regards to the vinegar trials, Norwich was not the only authority to trial its use. Bristol made national headlines because of the smell over its trial areas. Like these other authorities, we found it not to be effective against long rooted weeds.'

He said no 'equally effective and comparably priced' alternative to glyphosate-based products had been identified.'

Ms Carlo had pushed for a plant-based non-toxic foam called Foamstream to be tested in Norwich.

But Mr Maguire said: 'For Foamstream and other alternatives, as trialled both here and in other parts of the UK, test results are variable and inconclusive.

'In order to make an informed choice on replacing a herbicide that has been used effectively for 45 years, the council will need to see a persuasive body of evidence to support any proposed alternative.

'Typically this would need to be two to three years' worth of evidence which confirmed the long-term effectiveness.'