Shoppers in Scotland may soon have to pay at least 5p for a plastic bag in supermarkets under proposals to cut litter and protect the environment.

The bag tax is predicted to raise £5 million for charity and cut usage by up to 80%.

The Scottish Government is launching a three-month consultation this week on a range of proposals, including phasing out free carrier bags, with the aim of safeguarding Scotland's resources through efficient use of materials such as cutting waste and encouraging more positive environmental behaviour.

As part of a manifesto commitment to phase out free plastic bags in supermarkets, the Scottish Government will seek the public's views on phasing out free single-use carrier bags to encourage people to re-use them more.

The proposals are similar to the system brought in by the Welsh Government last October.

Early indications from Wales show carrier bag use has been cut by between 60% and 80% in supermarkets.

The Scottish Government consultation includes a proposal that retailers charge customers for all thin, disposable carrier bags – regardless of material – at a minimum of 5p.

Environment Secretary Richard Lochhead said: "Carrier bags are a highly visible aspect of litter. By reducing the amount being carelessly discarded, we can cut waste and its impact on our environment and economy.

"A small charge should also encourage us all to stop and think about what we discard and what can be re-used.

"This initiative will see retailers donating the proceeds to charitable good causes. It is hoped this could be up to £5m per year after retailers have covered their costs."

Green MSP Alison Johnstone said Scotland trails behind Wales and Northern Ireland in reducing bag waste and urged the SNP to explain why it waited almost a year to launch the consultation.

"The evidence from Wales is that a small charge is easy to implement and has a huge impact on shopper's behaviour, which can only be a good thing for litter in our towns and for our wildlife, seas and beaches," she said.

"Countries as diverse as Rwanda, Italy and Bangladesh have gone even further and have an outright ban on certain plastic bags because they recognise the negative impact that they are having. I ask those who oppose this policy to question whether there is such a thing as a free plastic bag. And who picks up the bill for littered cities and polluted seas?

"The SNP must now stop dragging its feet ... Greens will always fight for the strongest possible measures on waste because a zero-waste economy means more jobs and a better environment for all."

Conservative environment spokesman Jamie McGrigor said: "Scotland is a very wet country, particularly in the west, and using other types of carrier bags just isn't practical in the way it is in other European countries.

"People will feel that, after spending a significant amount of money on their weekly shop, this is just another expense.

"Somebody will be making good money out of this, because the production cost of a plastic bag won't be anything like 5p.

"I'm all for people reusing more sustainable bags, but my view is people who do should be handed incentives, rather than bringing punishment to those who do not."