The search for Malaysia Airlines Flight MH370, missing since March, and the hunt for four British yachtsmen lost in the Atlantic Ocean in May, has brought home to the British government the need to invest in maritime patrol aircraft, sources close to the matter say.

Since scrapping its former programme - the delayed and over-budget BAE Systems Nimrod MRA4 - as part of its defence review in 2010, experts say Britain has struggled to carry out aerial hunts for submarines as well as objects on the surface of its waters.

Adding further urgency is that a new aircraft carrier will be received by the Royal Navy in 2017; the vessel is part of a 6.2 billion pound project which Britain will want to adequately protect.

The two planemakers, which regularly battle over commercial orders, are now sparring over the maritime patrol market, in the expectation Britain will want to adapt existing planes to its needs, rather than opt for another complex project like Nimrod.

"It's less about the aircraft and more about what's in it," said Glynn Bellamy, partner and UK head of Aerospace and Defence at KPMG, explaining that unlike the specifically-designed Nimrod, a future project could use a cheaper aircraft but with high-tech kit onboard.

Both Boeing and Airbus say their options could suit Britain's needs.

Boeing brought its P-8A aircraft, based on the company's popular 737 commercial aircraft, to the Royal International Air Tattoo military air show last week and the Farnborough air show this week to show off what it describes as the plane's superior maritime surveillance and other capabilities.

Airbus is proposing an option around its C-295 military aircraft which it said could be configured to meet Britain's demands using UK suppliers for critical content, a factor it hopes will curry favour with a government which has stressed the importance of its domestic defence industry.

"We in Airbus Group want to be at the heart of providing options because obviously something like this, you'd want the UK industry to be as involved as possible," Airbus Group UK chief executive Robin Southwell said, adding the scale of the military patrol aircraft opportunity could run into billions of pounds.

"It's a big number," he said. "Acquiring, putting it in service ... then through life supportability and upgradability."

Airbus, which has provided a similar aircraft to Chile, said its option would be lower in cost compared with Boeing's P-8.

SPENDING REVIEW

After it cancelled the Nimrod programme, Britain assigned 30 UK air crew to maritime surveillance teams in the United States, Australia, Canada and New Zealand to ensure they kept their skills up-to-date, UK Master Aircrew Dave Miles told Reuters.

Miles, who is based at a naval air station in Maryland and is on loan with the U.S. Navy, is helping to lead testing of the P-8A aircraft and its software and hardware.

He said opting for a wholly new design, like another Nimrod-style project, instead of a proven one carried more risk that costs could spiral out of control.

Britain will undertake a new defence spending review in the second half of next year, when it could fire the starting gun for a maritime patrol aircraft competition.

"We continue to assess future requirements ahead of a decision in the next Strategic Defence and Security Review in 2015 and are considering a number of potential capability solutions," a spokeswoman for the Military of Defence said.

Industry sources suggest Britain's maritime patrol demands are unlikely to be straightforward. Maritime surveillance, search and rescue and submarine warfare capabilities could all form part of any tender, Southwell said.

"You link maritime patrol aircraft capability with Intelligence, Surveillance, Target Acquisition and Reconnaissance (ISTAR) capability so your maritime patrol aircraft can actually do far more," added independent defence analyst Howard Wheeldon.

Defence companies were buoyed by a UK government announcement on Monday that it would invest 800 million pounds in ISTAR, among other things, a shot in the arm following defence spending cuts of 8 percent over the last four years.

Other aircraft on offer with maritime patrol capabilities include a maritime surveillance offering from Boeing which uses a Bombardier Challenger 605 jet, or a version based on Lockheed Martin Corp's C-130 plane.

Victor Chavez, the chief executive of Thales Group's UK business, which provided the search radar on the old Nimrod, said the aircraft currently on the table could be a bridge to future surveillance by drones.

"In the medium to longer term, it could be probably be done by unmanned air systems," he said.

(Additional reporting by Kylie MacLellan and Victoria Bryan; Editing by Mark Potter)

By Sarah Young and Andrea Shalal