Ministers have been considering rolling out the plastic bag levy to all shops and doubling it to 10p.

The prime minister was reportedly planning to announce the proposals next week as part of a series of measures designed to encourage the reuse of carrier bags and reduce the UK’s reliance on plastics, which are harmful to the environment.

Reports in various Saturday newspapers suggested Theresa May was planning to open a consultation on the proposals to increase the charge and roll it out to all retailers, ending the exemption for those employing fewer than 250 people.

Downing Street declined to confirm the reports, which appeared in the Daily Telegraph, the Daily Mail and the Sun on Friday night, calling them “speculation”.

But May has previously spoken publicly about her desire to extend the existing scheme, which was introduced in 2015, in a bid to end what she termed Britain’s “throwaway culture”.

In a speech on the environment given in January, May pledged to consult on the plan. She briefed cabinet ministers, telling them the government had a clear belief in “conserving what is good, and standing against the profligate use of resources – whether it be public money or natural resources”, her official spokesman said at the time.

The plan was part of her attempts to realise the ambition of being the “first generation to leave the natural environment in a better state than we inherited”, the spokesman said.

Ministers also previously announced an intention to ban the sale of plastic straws, stirrers and cotton buds and plans for a deposit return scheme to increase recycling rates of drinks bottles and cans.

The number of disposable carrier bags issued by the seven biggest supermarket chains has declined by 86% since the charge was introduced, official figures have shown.

Donations from the bag levy to good causes totalled more than £58.5m last year, based on figures from the two-thirds of retailers that voluntarily reported the information.

A consultation on using the tax system to reduce waste is already considering measures such as introducing a “latte levy” on disposable coffee cups.