The number of wet wipes washing up on beaches in the UK increased by more than 50% last year, say conservationists, who have urged people to stop flushing them down their toilets.

The results of Marine Conservation Society’s (MCS) annual beach cleanup, released on Thursday, found the number of wet wipes more than doubled between 2013 and 2014. Thirty-five of the non-biodegradable cleaning cloths were found for every kilometre of beach.

The accumulation of wet wipes could be partly due to the severe rainfall during the 2013-14 winter. Choked sewers may have flooded more rubbish (including wet wipes) than usual into rivers, which ended up on beaches. But Charlotte Coombes, an MCS conservation officer, said there was a long-term increase in the number of cloths ending up in the environment and on beaches in particular.

Coombes said: “This move towards convenience, the move towards items to use once and throw away, it’s much easier for people to do that. What we are doing is not just using a lot more resources we are creating a lot more litter that can end up in the environment.”

Wet wipes are notorious for their impact on sewer systems, but the impact on ecosystems is also a concern. Coombes said five of the world’s seven remaining species of turtle regularly visit Britain’s waters to feed in the cooler, nutrient-rich seas. Turtles often mistake plastic bags for their natural jellyfish prey. But Coombes said wet wipes, which usually contain plastic fibres, posed a similar danger.

“When marine wildlife eats that plastic, which they quite often do, it just stays in the stomach of the animals and quite often they just die of starvation,” she said.

The predominant way for wipes to enter the environment is down peoples’ toilets. Some brands of wet wipe are marked ‘flushable’, but Coombes said: “Our sewerage systems weren’t built to cope with wet wipes. When flushed, they don’t disintegrate like toilet paper, and they typically contain plastic so once they reach the sea, they last for a very long time.”

Putting wet wipes down the toilet can cause blockages that lead to disgusting buildups of fat, known as “fatbergs”. In 2013 a lump of congealed fat the size of a bus was found in sewers beneath London. Earlier this year a spokesperson for Southern Water said Kent residents were dumping 2,000 tonnes of wet wipes into sewers. New York City has spent $18m (£12.3m) on “wipe-related equipment problems” in the past five years.

Blockages can also affect waterways by causing raw sewage to overflow into rivers and the ocean.

A spokeswoman for Keep Britain Tidy said the most sustainable option was to stop using wet wipes altogether, but failing that they should be disposed of appropriately.

A Wet Ones packet with advisory logo. Photograph: Energizer Group

“We didn’t have wet wipes 30 to 40 years ago. People just used flannels,” she said. “There’s three things that should go into a toilet. Putting it crudely, they are pee, poo and paper. Nothing else. Put it in the bin.”

During a weekend last September, more than 5,000 MCS volunteers gathered and catalogued 2,457 pieces of litter for every kilometre of coastline they scoured. This was an increase of 6.4% from 2013.

MCS said the government should act to halt the increase in beach rubbish. The society called for a policy that targeted the main sources of marine litter – the public, fishing, shipping and sewage-related debris (including wet wipes).

The increase in litter was not uniform. The south-west saw an increase of89% in litter, in Wales the increase was 46%. In Scotland and northern England less rubbish was found than in 2013.

A spokeswoman for Energizer Group, which manufactures Wet Ones, said the company includes a logo on the packaging advising customers not to flush them down the toilet.