An RAF officer faces a court martial for refusing to serve in Iraq on the grounds that the invasion of the country was illegal, defence officials said yesterday.

Flight Lieutenant Malcolm Kendall-Smith, a medical officer based at Kinross, in Scotland, faces four counts of disobeying a lawful command under the 1955 Air Force Act.

He is the first British officer to face charges on these grounds and his prosecution is likely to add to growing unease among the military about the war in Iraq. He may face a jail sentence, though senior military officers, concerned about the effect of Iraq on the morale of British armed forces personnel, will not relish the prospect of a martyr and another focus of opposition to the war and invasion of Iraq.

The 37-year-old lieutenant, who was decorated for service in Afghanistan and Iraq, believes the invasion was illegal, defence sources said.

A key part of his case, according to reports yesterday, will be that under RAF law an officer is justified in refusing to obey commands if they are illegal. The Queen's commission requires armed forces officers to act according to "the rules and discipline of war". Defence sources suggested the officer also had a conscientious objection to the war.

Some reservists have refused to serve in Iraq, but this is the first time that a full-time officer has objected.

The case of Flt Lt Kendall-Smith, who has dual UK-New Zealand nationality, is now before the RAF's prosecuting authority. The Ministry of Defence said no date had been set for his court martial.