A mystery that has perplexed environmental campaigners in a French coastal town for decades has finally been solved.

Garfield telephones have been washing up on Brittany’s Iroise coast since the 1980s – with the coastal community stumped as to where they were coming from.

Thousands of the phones were manufactured in the 80s – complete with a feature that sees the famous cat opening his eyes when you pick up the receiver.

Locals patrolling the beaches have been picking up the fragments of the handsets for years and they were used as a symbol of ocean plastic pollution during an environmental campaign last year.

It was the campaign that finally cracked the case.

Local farmer René Morvan saw the advertisements and remembered finding some when he was about 19 or 20-years-old.

He suspected they were coming from a secluded cave that could only be reached at low tide.

"You had to really know the area," he told Franceinfo.

"We found a container that was stranded in a fault. It was open - a lot of things were gone, but there was a stock of phones.

"At the time, there was a lot of things that came to us from the sea."

Garfield phone fragments washed up on Brittany beaches. Image: Martine Dominique/Ar Viltansou/Facebook

Members of Ar Viltansou environmental group, along with Franceinfo journalists, went off to look for the container.

Climbing down rocks covered with seaweed towards a cave, they spotted pieces of the destroyed container's shell and, wedged between some rocks, Garfield phones.

Ar Viltansou President, Claire Simonin-Le Meur told Euronews: “We found this incredible cave, that was 30 metres deep and right at the end the remains of the container.”

“At the cave opening there was a Garfield lodged in the roof, so we knew we weren’t mistaken and this was where they were.”

Garfield phone fragments washed up on a Brittany beach. Image: Martine Dominique/Ar Viltansou/Facebook

Campaigners long suspected the phones may be coming from a lost shipping container – as it is believed at least 1,500 containers them fall overboard from cargo ships every year.

Ms Simonin-Le Meur said the mystery may yet have another twist in the tail.

Judging by the locations of the beaches where the phones washed up, she said, it may well be that more than one container fell into the sea.

Garfield phone. Image: Martine Dominique/Ar Viltansou/Facebook