Plastic straws and cotton buds could be banned in England as part of the government’s bid to cut plastic waste.
Ministers pointed to one estimate that 8.5bn plastic straws were thrown away in the UK every year.
The prime minister said plastic waste was “one of the greatest environmental challenges facing the world”.
And Theresa May will urge leaders at the Commonwealth Heads of Government Meeting, which began earlier, to follow the UK’s lead in tackling the problem.
The Queen has formally opened the summit at an event at Buckingham Palace attended by prime ministers and presidents from the 53 states that make up the organisation.
Mrs May claimed the UK was a “world leader” on tackling plastic waste, highlighting the charges that have been introduced for plastic bags, the ban on microbeads and the announcement in March of a consultation on introducing a deposit return scheme for drinks containers in England.
“Alongside our domestic action, this week we are rallying Commonwealth countries to join us in the fight against marine plastics,” she said.
“The Commonwealth is a unique organisation, with a huge diversity of wildlife, environments and coastlines.
“Together we can effect real change so that future generations can enjoy a natural environment that is healthier than we currently find it.”
Analysis: By BBC science editor David Shukman
The environment secretary Michael Gove describes plastic waste as a worldwide emergency, which naturally raises questions about the speed of the government’s response.
The headlines talk of a ban on plastic straws – but the announcement is about a consultation to do that. A similar exercise is under way about a deposit scheme for plastic drinks bottles, and MPs were not impressed on Wednesday when they learned that the system itself will not come into effect until 2020.
When ministers talk of the UK leading the world on this hot topic it’s worth casting an eye over the actions of other countries. Dozens have actually banned plastic bags – Britain has a system of retailers having to charge for them.
And since last year Kenya has adopted the most draconian measures of all: there are fines if you use a plastic bag and if business people are caught making or importing them, they actually face up to four years in jail.
Amid many claims about fighting a war on plastic, the Kenyans are leading the charge.
It comes as 60 UK music festivals, including Bestival in Dorset and Boomtown in Hampshire, have said they will ban plastic straws at their events this summer.
Bestival’s co-founder Rob Da Bank said they were “leading the global charge against unnecessary plastic”, as the group of festivals also pledged to eliminate all single-use plastic by 2021.
Environment Secretary Michael Gove, who trailed the idea of banning plastic straws in February, will launch the consultation later this year.
“We’re going to consult on what the best way is in order to get rid of straws, get rid of stirrers and also get rid of plastic stemmed cotton buds that we use so many of,” he told BBC Radio 4’s Today programme.
“It’s a worldwide emergency – that’s why we’re choosing to act. It’s also why we’re working with other Commonwealth countries.”
He said a consultation was necessary, particularly in relation to straws, because there were some disabled people who need to use plastic straws.
Mr Gove said a number of retailers, bars and restaurants were already cutting plastic use, with the plastic bag ban set to be extended from major retailers to all retailers.
Scotland’s Environment Minister Roseanna Cunningham announced earlier this year a plan to ban plastic straws, following a similar move aimed at banning the sale and manufacture of plastic-stemmed cotton buds.
Greenpeace UK and Friends of the Earth have welcomed the announcement as a “step forward” but both also warned more action would be needed.
Greenpeace’s Louise Edge said other non-recyclable “problem plastics” should also be banned at the earliest opportunity and retailers must take responsibility to phase out single-use plastics in their own products.
Friends of the Earth’s Julian Kirby said the “only long-term solution is a complete phase-out of all but the most essential plastics”.
The news was welcomed by the Green Party, but co-leader Jonathan Bartley said the government “must see these plans through to action, and bring forward the utterly un-ambitious target of eliminating all avoidable plastic waste by 2042”.
Earlier this week, Mrs May announced the new Clean Oceans Alliance – an agreement between the UK, Vanuatu, New Zealand, Sri Lanka and Ghana, which pledged to ban microbeads cosmetics and cut plastic bag use by 2021.
To fund it, she also assigned £61.4m for global research and to improve waste management in developing countries.
The Queen will be joined by other members of the Royal family at the formal opening of the Commonwealth Heads of Government Meeting (CHOGM) on Thursday morning.
BBC royal correspondent Jonny Dymond said it would be “emotional” for some, because it could be the last CHOGM the Queen opens – she has stopped travelling long distances and the event is unlikely to return to London for some time.
“The Commonwealth has been nurtured by the Queen over the decades and it holds a special place in her affections,” he said.
“That affection is reflected among the heads of government, who often send a more junior representative to the meeting – this time around it is prime ministers and presidents.”
A number of events have already taken place ahead of the first official day of the CHOGM, including a Commonwealth Youth Forum, attended by Prince Harry and Meghan Markle.
Mrs May also met Caribbean leaders on Tuesday to apologise for the fiasco around threats of deportation to the Windrush generation, who legally settled in the UK 70 years ago.