More than two million plastic bags are handed out by small shops every day which would not be used if the charge was increased to 10p and levied on every business, figures suggest.
The 5p levy on plastic bags was introduced in England in 2015, with the most recent figures showing large retailers sold 1.7 billion single-use carrier bags in 2017-18.
Small businesses – defined as those employing 250 people or fewer – are exempt from the charge.
The Department for the Environment, Food and Rural Affairs previously said the levy had taken more than 15 billion bags out of circulation – and said it planned to increase the charge to 10p and include all retailers, potentially from January 2020.
Lord Gardiner of Kimble, a government environment minister, said 3.6 billion plastic bags were handed out by small businesses in 2017.
In response to a written question by Lord Hayward of Cumnor, he said: “We estimate that the policy to increase the charge to 10p would cause a decline in consumption of SUCBs (single use carrier bags) in MSMEs (micro and small businesses).
“(This is) assumed to be 23% in the first year of change and 80% within three years (2020-2022).”
But Lord Hayward said these estimates were too conservative and urged the government to extend the charges sooner.
He told The Times: “We have now been waiting for over a year and a half.
“These figures confirm that for each day the policy is delayed some 2,250,000 bags are used which would not be used if there were a charge.
“If the impact was to reduce usage by 50%, which I believe is more likely, 4,500,000 bags a day would be taken out of waste streams.”
Retailers are expected to donate any proceeds from the 5p charge to good causes and 153 companies reported donations of £51.6 million in 2017/18, figures show.
Of this, £20.5 million went to causes local to the businesses, £20.4 million to charities or voluntary organisations, while £2.9 million went to support environmental issues.
Similar plastic bag levies have been introduced in Wales, Scotland and Northern Ireland.