A big drop in plastic bags found in the seas around Britain has been credited to the introduction of charges for plastic bags across Europe.

Ireland and Denmark were the first two countries to bring in levies for plastic bags from shops in 2003, followed by slew of other European countries. England was the last UK nation to introduce one, in 2015.

In the first such study of its kind, scientists have found an approximately 30% drop in plastic bags on the seabed in a large area from close to Norway and Germany to northern France, and west to Ireland.

The authors of the study, published in the journal Science of the Total Environment, claim the drop in plastic bag pollution, measured from 2010 – about the mid-point of charging policies coming into force – showed the power of such levies.

“The fewer bags we use, the fewer we can lose, the fewer we can put into the environment,” said Thomas Maes of the Centre for Environment, Fisheries and Aquaculture Science, lead author of the paper.

“If we all work together towards a better environment, we can make changes. A lot of people live in doom, but … don’t give up yet.”

The results could also be used by campaigners for other charges aimed at reducing public problems, such as pollution, obesity, smoking and congestion. The UK is already consulting on a refundable charge for bottles and cans.

“These findings have reminded us of one of the fundamentals of policy – incentives matter,” said Robert Colvile of the Centre for Policy Studies, a rightwing thinktank.

“When it comes to the environment in particular, pricing in external costs is better than heavy-handed regulation,” he said.

Globally around 8m tonnes of plastics enters the marine environment every year – the weight of more than 80 of the largest aircraft carriers. They are blamed for ensnaring sealife and birds, and have been found in the guts of dozens of species.

A UK levy of 5p per bag introduced in 2015 has already reduced single-use plastic bags given out by major retailers by 85% – down from 140 to 25 bags for the average person each year.

The policy applies only to major retailers, but government is consulting on extending it to almost all shops.

The marine pollution study has been trawling the seabed for 25 years, recording the number of items of pollution found in each square kilometre. Two-thirds of all trawls have found at least one item of plastic, and while the number of plastic bags has fallen, other plastic pollution has increased, especially fishing gear.