Bristol could become the first major city in England to collect black waste bins every four weeks, under new plans, the city council says.

The Green Party-led authority already has the highest recycling rate among “core cities” in England, with 45% of household waste being recycled. It has begun a public consultation on potential changes to three-weekly or four-weekly collections until 10 March.

The authority’s deputy leader, Heather Mack, said the move would reduce the cost and “the impact on the environment”, but opposition councillors said there were increasing complaints about the existing service, which should be sorted first.

Many English local authorities already have three-weekly collections.

Switching to a three-weekly black bin collection will save the council £1.3m a year, while a four-weekly collection would save £2.3m, the council says.

The move has been proposed to encourage more recycling of food waste.

Bristol City Council said around 50% of households do not recycle food waste, and a quarter of most black bin rubbish is food, which could be recycled.

Around £700 of food is thrown away every year per household, the council added.

Food waste is sent to an anaerobic digestion plant and converted into energy by burning the methane waste that comes from it, with the by-product being used for farm fertiliser.

The council is also facing increasing costs of treating waste, which has increased by £4m in the last five years.

Ms Mack said: “There’s due to be a tax on the residual waste we send to be processed, for the carbon in that.

“So we really need to consider how much we’re sending and where else could it go.

“We would also offer larger bins for larger households, and an extra collection for people with sanitary products or nappies, so we don’t want people to unduly struggle with this,” she added.

The plans have been criticised by opposition parties at City Hall.

Tom Renhard, leader of the Labour group, said: “There needs to be a focus on sorting out the existing service.

“I’m getting an increasing number of complaints from local residents across the city that recycling isn’t being collected and black bins aren’t being collected on [the current] two-weekly basis.

“Some of my residents haven’t had a recycling collection this side of Christmas.

“You’re also starting to see that if residents’ recycling isn’t getting collected and it’s piling up, they’re going to put it in the bin, which isn’t going to help recycling rates.”