Analysis of the samples by scientists at the University of Exeter using an infrared detector found microplastics were in 28 out of 30 locations tested.

A total of 1,271 pieces of plastic ranging from fragments of straws and bottle tops to tiny microbeads less than 1mm across in size were fished out of the rivers.

Greenpeace said the concentrations of plastic waste in the Mersey were recorded at 2 million microplastics per square kilometre, making it proportionally more polluted than the Great Pacific Garbage Patch.

Greenpeace ocean plastics campaigner Fiona Nicholls said: “When processing the samples, I remember thinking that this was an outrageous amount of microplastics, just hundreds and hundreds of microplastics nestled among the twigs, leaves and feathers that were also making their way down the river.

“During this campaign we witnessed voles eating plastic, swans using it to build their nests, and caddisfly larvae using it to make their protective casings.”

She added: “Fiddling around the edges of the plastic pollution problem by banning straws simply doesn’t cut it.

“We need to see bold new plastic reduction targets in the upcoming environment bill, and aim to at least halve single-use plastic production by 2025.”

Anyone who’s seen the aftermath of festivals will know that it can end up looking more like a rubbish tip than a celebration of music. 

About 23,500 tonnes of waste are produced each year at UK music festivals, according to Powerful Thinking – a group which looks at the festival industry. Roughly two thirds of that goes into landfill.

But Glastonbury co-organiser Emily Eavis hopes measures the team there has taken will inspire fans to be greener at this year’s event.

“Sustainability and the need to live in harmony with the land, has always been vital to Glastonbury Festival,” Emily told the Press Association.

Single-use plastic bottles have been banned on site, anyone going to the festival has been asked to asked to leave non-essentials at home and non-compostable plates, cups, straws aren’t allowed either.