The 5p charge on plastic bags to be introduced in October faces accusations that it will confuse customers - and doubtless lead to arguments at the checkout.

The charge is being introduced as part of a government policy to reduce waste by cutting bag use by up to 80 per cent in supermarkets and by half on the high street, with the aim of reducing litter and protecting wildlife.

The new rules are likely to baffle shoppers and cashiers alike, as till operators will be the ones to decide whether the charge must be paid.

But before they charge you, they have to ensure the bag ‘qualifies’ as a bag.

The government has issued guidelines defining what a plastic carrier bag is: it must be made of plastic, be unused, have handles and be 70 microns thick or less.

Cashiers must then check if the items in your shopping qualify for a free plastic bag.

Guidelines issued by the Department for Environment, Food and Rural Affairs (Defra) note that you can receive a free plastic bag if your shopping includes items from a long list of exemptions, including: uncooked fish, meat and poultry products, unwrapped blades and “live aquatic creatures in water”.

Also included are flowers, bulbs, potatoes and prescription drugs.

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The exemptions also apply to unwrapped food for human or animal consumption, such as chips and food sold in containers that could leak.

However, if even one non-exempt item is placed in the bag, cashiers must charge 5p.

The guidelines explain: “For example, you wouldn’t charge for a bag containing an unwrapped blade and unwrapped loose seeds, but adding a box of cornflakes means you’d have to charge.”

As comical as it sounds, the new charge could have serious consequences: retailers who fail to detect shoppers who need to pay for their plastic bags could face fines of up to £5,000 if they are caught by local authority inspectors.

In another confusing twist, shop owners with fewer than 250 employees are not required to charge for their bags.