Two New Zealanders have written a book claiming they know what happened to missing flight MH370.

Aviation expert and head of the now-defunct Kiwi Airlines Ewan Wilson and journalist Geoff Taylor believe the pilot committed suicide - killing all 239 onboard in March.

The pair are in Britain speaking to aviation experts.

They claim Zaharie Ahmad Shah locked his co-pilot out of the cockpit, de-pressurised the cabin and shut down all communication links before turning the plane around.

They believe he made eight different course changes before flying on auto-pilot before a controlled ditching in the sea, explaining why no debris has been found.

The theory is the result of the first independent study into the disaster.

The claims are made in the book 'Goodnight Malaysian 370', the culmination of a four-month study.