Britain on Wednesday said it intended to create what will be the world's biggest fully-protected marine reserve, covering an area nearly the size of France and Germany put together in the Pacific Ocean.

The reserve will be based around the remote Pitcairn Islands archipelago, a British overseas territory that is inhabited by descendants of the sailors who staged a famous mutiny on the Bounty ship in 1789.

"The government intends to proceed with designation of a MPA (Marine Protected Area) around Pitcairn," read the budget unveiled by finance minister George Osborne in parliament.

But the government said a final deal would depend on agreements for satellite monitoring of the vast area, preventing ports from landing illegal fish catches and naval patrols.

The Pew Charitable Trusts, the US charity that has led the campaign for the reserve, said the area would cover 834,334 square kilometres (322,138 square miles).

It is home to at least 1,249 species of marine mammals, seabirds and fish and includes the world's deepest known living plant -- a species of encrusting coralline algae found at a depth of 382 metres.

"The new reserve protects some of the most near-pristine ocean habitat on Earth," Pew said in a statement.

In 2013, Pew, National Geographic and the local elected body on the remote archipelago, the Pitcairn Island Council, submitted a proposal for the creation of the reserve.

"The Pitcairn Islands Marine Reserve will build a refuge of untouched ocean to protect and conserve a wealth of marine life," said Matt Rand, director of Pew's Global Ocean Legacy project.

Pitcairn was settled in 1789 by mutineers from the British naval ship the Bounty, who famously set their captain William Bligh adrift in the South Pacific.

Many of the families of the mutineers moved from Pitcairn, a five-square-kilometre island midway between New Zealand and Chile, to the larger Norfolk Island in 1856.

Enric Sala, National Geographic's explorer-in-residence, a member of a scientific expedition that visited the islands, said the move "will protect the true bounty of the Pitcairn Islands -- the array of unique marine life in the surrounding pristine seas."

Pew said the area would be monitored with a satellite monitoring system known as the "Virtual Watch Room" that will allow the detection of illegal fishing activity in real time.

"This is the first time any government has combined creation of a marine reserve with the most up-to-date technology for surveillance and enforcement of a protected area," Pew said.

Pitcairn would be the largest continuous protected area of ocean around the world.

The Pacific Remote Islands Marine National Monument announced by US President Barack Obama last year covers a bigger sea surface -- 1.27 million square kilometres -- but is made up of different areas.

British actress Helena Bonham Carter, who recently posed naked with a tuna to support the campaign for marine environmental protection, said the move would allow threatened fish species to regenerate.

"We won't have to explain to our great-grandchildren what a tuna was," she said, adding: "I never knew taking my clothes off could be so effective. I must do it more often."