Britons’ love of novelty Christmas jumpers is helping to fuel the world’s plastic pollution crisis, a report has warned.

Whether emblazoned with flashing lights or alpine motifs, 12m jumpers are set to be snapped up this year, despite 65m already languishing in UK wardrobes.

But as well as triggering huge levels of waste, the research by the environmental charity Hubbub has shown that most new sweaters contain plastic. Its analysis of 108 garments on sale this year from 11 high street and online retailers – including Primark, George at Asda and Topshop/Topman – found that 95% of the jumpers were made wholly or partly of plastic materials. The charity said the garment had become one of the worst examples of fast fashion, now recognised as hugely damaging to the environment.

With so-called Christmas jumper day – an annual publicity push by the charity Save the Children – looming on Friday 13 December, millions of consumers are expected to scour shops for eye-catching festive woollies.

Hubbub’s research found that two out of five Christmas jumpers are only worn once over the festive period, and one in three adults under 35 buys a new Christmas jumper every year.

The plastic fibre acrylic was found in three-quarters of the jumpers tested, with 44% made entirely from acrylic. However, only 29% of consumers realised that most Christmas jumpers contain plastic.

A recent study by Plymouth University found that acrylic was responsible for releasing nearly 730,000 microfibres per wash, five times more than polyester-cotton blend fabric and nearly 1.5 times as many as pure polyester.

Sarah Divall, the project coordinator at Hubbub, said: “We don’t want to stop people dressing up and having a great time at Christmas but there are so many ways to do this without buying new. Fast fashion is a major threat to the natural world and Christmas jumpers are problematic as so many contain plastic. We’d urge people to swap, buy secondhand or rewear, and remember a jumper is for life not just for Christmas.”

Its tips for eco-friendly options include customising existing sweaters and hunting for charity shop and vintage bargains.

On behalf of the retailers in the study, Leah Riley Brown, a sustainability policy adviser at the British Retail Consortium, said: “Consumers can be assured that, on average, the clothes they are purchasing have lower environmental impacts. Retailers are making strides to ensure old clothes can be turned into new ones for a more circular economy. They are creating more takeback schemes so clothes can be reused and recycled to divert them away from landfill.”