"Mud matters," said Tom Brook, ocean conservation specialist at WWF which produced the report.

"Saltmarshes are powerful natural allies in the fight against climate change -- storing carbon, protecting our coasts and supporting rich biodiversity," he added.

Saltmarshes occur where the land meets the sea, and help absorb wave energy and the impact of storms, acting as natural flood barriers.

They also "are highly efficient at capturing and storing carbon, playing a vital role in mitigating climate change," the report said.

Britain has lost some 85 percent of its saltmarshes since 1860, much of it being drained to convert into farmland, or degraded by pollution and rising sea levels.

The remaining 45,000 hectares play a key role in protecting coastal areas.

They also provide habitats for migratory birds in estuaries such as around the Thames in the southern UK, as well as the Severn which flows through England and Wales, the northeastern Humber and the western Solway Firth.

The WWF research, carried out with insurance firm Aviva and the UK Centre for Ecology & Hydrology, "adds to a growing body of evidence showing that saltmarshes are not just ecologically important but essential to building a resilient, net zero future," said Brook.

The WWF, one of the world's leading conservation organisations, is now calling for saltmarshes to be included in the UK's greenhouse gas inventory.

The inventory records annually how much carbon is emitted into the atmosphere and how much is removed, as the UK seeks to reach net zero by 2050.

The research findings are based on data collected from a pioneering solar-powered "carbon flux tower" set up on the Ribble river estuary in northwestern Lancashire.

It monitored the exchange of carbon dioxide and other gases between the saltmarsh and atmosphere, capturing how much carbon is absorbed or released throughout the year.

The data revealed that the saltmarsh is a significant "sink" locking away greenhouse gases such as carbon dioxide.