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."

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.

And a spokesman for the Welsh Government indicated it would also consider a ban: "We would welcome collaboration from the UK government on any action on banning straws. We will work with Defra to look at how this can be done effectively in Wales."

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.