The embattled Liberal candidate for the crucial Longman by-election often refers to himself as a 'Major' despite only rising to a low-level ranking in the Australian Defence Force.

Trevor Ruthenberg, who has this month apologised for wrongly claiming to hold a distinguished military medal, previously served in the Royal Australian Air Force rising to the third lowest rank of corporal.

Despite that, the Liberal National Party's flag bearer for the seat of Longman, north of Brisbane, often refers to himself as a 'Major' or a 'Captain' in the Australian Army Cadets.

An LNP spokesman said Mr Ruthenberg was given the honorary rank of Major when he commanded the 14th Battalion of the Australian Army Cadets.

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The Liberal candidate for the crucial Longman by-election often refers to being a Major despite having a low-level ranking in the Australian Defence Force

A Department of Defence spokeswoman said a RAAF corporal could also hold a higher position in the Cadets.

'It is possible for an individual holding the rank of Corporal in the Royal Australian Air Force to subsequently or simultaneously hold a rank such as Major in the Australian Army Cadets,' she told Daily Mail Australia.

Queensland Liberal National Party campaign director Lincoln Folo said Mr Ruthenberg was given his honorary rank of Major when he commanded the 14th Battalion of the Australian Army Cadets, as is standard for the volunteers who serve as Cadet Battalion commanders.

'Trevor's fulltime paid service in the RAAF is completely unrelated to his voluntary service in the cadets,' he said.

'His rank as Corporal in the RAAF has nothing to do with his role in the Cadets.'

After serving in the RAAF for six-and-a-half years, Mr Ruthenberg told reporters last week he became a commanding officer in the Australian Army Cadets.

In this role, the LNP candidate has referred to himself as a 'Major'.

Trevor Ruthenberg previously served in the Royal Australian Air Force rising to the third lowest rank of corporal

He touted this title on the website of the Mosaic Property Group, where is the chief executive of the community relations arm of the company, the Mosaic Foundation.

'Fun facts. Attention: in his spare time he's known as Major Ruthenberg of the Australian Army Cadets,' it said.

On the Military Cadets Facebook page for the Sandgate division, in Brisbane's north, Mr Ruthenberg was pictured in 2015 wearing a military uniform with a 'Captain' insignia.

Mr Ruthenberg was recently forced to admit to falsely claiming to hold an Australian Service Medal, which is awarded for distinguished service in a non-warlike situation overseas.

The factual error had been published on the Queensland Parliament website since 2012, after he was elected as the state member for Kallangur for one term as a Liberal National Party MP in Campbell Newman's government.

The Liberal National Party's flag bearer for Longman, north of Brisbane, often refers to himself as a Major and a Captain

He has since had the record corrected to say he was given an Australian Defence Medal, which is awarded to those who had served in the military for four years.

'I said that I had an Australian Service Medal when in fact I had an Australian Defence Medal,' he told reporters.

'I've never claimed to have served overseas, I've never worn an Australian Service Medal, I've only worn the medal that was awarded to me which was the Australian Defence Medal.'

Mr Ruthenberg touted his 'major' title on the website of the Mosaic Property Group, where is the chief executive of the community relations arm of the company, the Mosaic Foundation

In that same media conference, he said he had taught his cadets to own up to their mistakes.

'I always tell my cadets that when you make a mistake, you need to stick your hand up and own it,' he said.

The Longman candidate, who is favoured to win the marginal seat off Labor at this Saturday's by-election, said he had joined the cadets to impart his wisdom to the next generation of military leaders.

'I subsequently served as a commanding officer in the Australian Cadet corp trying to pass on some of that experience to the young people,' he said.

Were Mr Ruthenberg to prevail in Longman, Prime Minister Malcolm Turnbull's government would become the first in 98 years to win a seat off the opposition at a by-election.

By-elections are also being held this Saturday in Tasmania, South Australia and Western Australia, after three other first-term MPs were found to be dual British citizens, making them ineligible to sit in federal parliament.