Supermarkets and other big stores in England are to introduce a 5p charge for plastic bags.
The move is due to be announced this weekend by Deputy Prime Minister Nick Clegg at the Liberal Democrat conference in Glasgow.
It will bring England into line with the rest of the UK - with charges already in place in Wales and Northern Ireland, and Scotland set to follow suit in 2014.
Lib Dem sources said the charge, intended to discourage use of the environmentally damaging bags, would come into effect in England in 2015.
However, it is not yet clear whether it will be before the general election, set for May that year, or after.
Mr Clegg was said to have had to fought hard within the Coalition for the scheme - which is Lib Dem party policy - at a time when ministers are under intense pressure over rising cost of living.
But with a 76% fall in plastic bag use in Wales since the levy was introduced there in 2011, the Lib Dem leader was said to believe that it was the right thing to do.
A Lib Dem source said the charge would be the "centrepiece" at the conference this weekend.
Energy and Climate Change Secretary Ed Davey told Sky News: "Liberal Democrats in the coalition are pushing the green agenda all the time.
"Sometimes it's quite a fight - this one we've won and it's very clear the evidence shows that plastic bags not only create lots of litter and a real eyesore, but they can be really bad for wild animals, particularly marine life."
The charge will only apply to supermarkets and other large stores, with small corner shops excluded.
The proceeds will go to charities involved in clearing up the environmental damage caused by the bags rather than the Government or the retailers.