The commitment is part of the government's 25-year plan to improve the natural environment.

"I think people will be shocked at how today we allow so much plastic to be produced needlessly," the PM said.

But green groups are angry the proposals will have no legal force - and Jeremy Corbyn said 25 years was "far too long" to take action.

The Labour leader said the "throw-away" culture had to be tackled "now," after his party described Mrs May's plans as a "cynical attempt at rebranding the Tories' image".

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Under the government's plan, supermarkets will be urged to introduce "plastic-free" aisles while taxes and charges on single-use items such as takeaway containers will be considered.

Mrs May's announcements, which have been agreed by cabinet, also include:

• Confirmation of the extension of the 5p charge for plastic carrier bags to all retailers in England
• Government funding for plastics innovation
• A commitment to help developing nations tackle pollution and reduce plastic waste, including through UK aid

In her speech, Mrs May said: "We look back in horror at some of the damage done to our environment in the past and wonder how anyone could have thought that, for example, dumping toxic chemicals into rivers was ever the right thing to do."

She called plastic waste "one of the great environmental scourges of our time", adding: "In the UK alone, the amount of single-use plastic wasted every year would fill 1,000 Royal Albert Halls."

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Asked after her speech about her own environmental credentials, she revealed she had put owl and bat boxes in her garden.

Meanwhile, plans to help more children engage with the environment will include £10m for school visits and a programme to create school grounds that allow youngsters to learn more about the natural world.

Mrs May said she would put the oceans firmly on the agenda of the Commonwealth Heads of Government Meeting in April.

Analysis by the BBC's Roger Harrabin

Thursday's announcements are the culmination of an environmental week for the government. On Sunday, Mrs May promised a clampdown on plastic waste. On Wednesday, plans emerged to extend the 5p plastic bag charge to include corner shops in England.

Ministers have been under political pressure to do more for the environment after it was identified by the Tory think-tank Bright Blue as the key issue for young voters, who failed to back the party in large numbers at the 2017 general election.

Environmentalists agree that the government's plan to restore nature - not just safeguard nature - is genuinely radical.

Many of the UK's landscapes have been ravaged by development, intensive farming and sheep grazing. Only 2% of wildflower meadows have survived.

I understand that the document will cover many policy areas, including: managing land sustainably; enhancing nature and recovering wildlife; increasing people's health and well-being through nature; resource efficiency, reduction of pollution and waste and protecting and improving the global environment.

But there is scepticism about how far the environment department Defra will be able to carry out its plans.

There are huge pressures on the natural world from urgently needed house-building; HS2 threatens scores of ancient woodlands; and the Department for Transport has a major road-building programme.

Earlier Environment Secretary Michael Gove told the BBC he wanted the government to "set the global gold standard" on the environment.

He also said ministers were "reflecting" on a proposal from a Commons committee for a 25p charge on disposable cups.

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Green campaigners said Mrs May's plans could simply be shelved if they become inconvenient and the promise to stop "avoidable" plastic waste is too vague.

Greenpeace said Mrs May's announcement was a "missed opportunity", questioning why there was no mention of deposit return schemes for bottles, while Friends of the Earth said a "clear timetable" not "woolly promises" were needed.

Sue Hayman, Labour's environment spokeswoman, said the Conservatives had a record of "failure and broken promises" on the environment.

She said the "weak" proposals would mean the problem with plastic waste was "kicked into the long grass".

The Liberal Democrats said it "beggared belief" that a target of 2042 had been set for removing plastic waste and that action was needed now.