Amazon has been criticised by environmental groups and customers after introducing a range of plastic packaging that cannot be recycled in the UK.

While supermarkets and other retailers have been reducing their use of single use plastics, the world’s biggest online retailer has started sending small items in plastic envelopes, seemingly to allow more parcels to be loaded on to each delivery truck.

Adrian Fletcher, an Amazon customer from Glasgow, is among a number who have complained to the company. He said the move felt like a “major step backwards” in the fight against plastic.

“My husband is disabled, and we rely a lot on Amazon and other home deliveries. Previously our small orders arrived in easily recyclable cardboard packaging, but a few months ago Amazon started using plastic envelopes. I diligently recycle all the packaging but can’t these,” he said.

“The supermarkets have all been dropping carrier bags from their online deliveries, but Amazon is going the other way – it’s madness. I have asked them not to ship my orders using plastic packaging but this falls on deaf ears.”

Amazon’s Second Chance website, which details how customers should recycle its packaging, states the Prime-branded envelopes are “not widely recycled across the UK”.

It is thought that Amazon ships between 4bn and 5bn parcels a year worldwide. In February, the Washington Post reported on how the new Amazon envelopes were clogging up US recycling centres as consumers were wrongly placing them in recycling bins.

On Monday, Amazon was among 181 companies that signed up to a new official definition of corporate purpose in the US, which threw out the decades-old sole objective of making as much profit for shareholders as possible to embrace the interests of other stakeholders, including employees, customers, suppliers and the community.

The move, seen as a response to increasing criticism of business and traditional capitalism, included a pledge to protect the environment “by embracing sustainable practices”. It was signed by Jeff Bezos, the Amazon founder and boss.

Mike Childs, the head of policy at Friends of the Earth, said: “Despite the huge public outcry, it’s astonishing how many companies are still using single-trip, unrecyclable plastic for deliveries.

“If we want to stem the tide of plastic pollution blighting our environment, giant firms like Amazon have to find ways of making deliveries in returnable and reusable packaging. And if they won’t – the government should make them.”

This month the new environment secretary, Theresa Villiers, claimed society “was calling time on being “throwaway” after the publication of figures showing how single-use plastic bags had fallen out of favour.

The figures from the Department for the Environment, Food and Rural Affairs showed the number of single-use plastic bags sold in the main supermarket chains had fallen by more than 90% since the introduction of the 5p charge in October 2015.

Amazon told the Guardian: “Our mission is to deliver the very best customer experience. We work with manufacturers worldwide to continuously improve packaging design and introduce new, sustainable packaging that delights customers, eliminates waste, and ensures products arrive intact and undamaged for our customers.” It also said it listened to its customer feedback.