A driver who says he drove safely a day after consuming a small amount of cannabis, and was no longer under the influence at the time of an accident another day later, has lost a claim dispute.

The Allianz policyholder says the accident, which happened just after midnight, occurred because he veered to avoid a head-on collision with a car – or possibly two - straddling the middle line with bright headlights.

While driving home after seeing his girlfriend, he says he saw headlights approaching from the other direction with high beams on.

He was blinded by the oncoming traffic and swerved to the left, mounted the kerb and collided with a postbox, causing his airbags to deploy. He blacked out and then hit a power-line pole. His vehicle was deemed a total loss.

Relying on expert opinion, Allianz declined the claim on the basis he was under the influence of cannabis at the time of the accident, which the policy excluded.

Emergency services and police attended the scene and after a breathalyser test returned a negative result he was taken to hospital, where blood test results showed delta-9-tetrahydrocannabinol (THC) in a concentration of 23 micrograms per litre two hours after the accident.

The motorist told the Australian Financial Complaints Authority (AFCA) he had consumed a small amount of cannabis two days earlier and had driven safely on the day before the 12.15am accident. He denied smoking cannabis in the 24 hours leading up to the crash, saying the evasive action he had to take to avoid hitting the oncoming car was the cause, not intoxication.

AFCA said Allianz had established he was likely under the influence at the time of the collision and this caused or contributed to the loss.

"The concentration of THC would significantly impair the ability to maintain road position, avoid potential hazards and to stop safely. Accordingly, the panel finds that the insurer is entitled to rely on the exclusion clause to deny the claim,” AFCA’s ombudsmen said.

On the claim form, the motorist said he had not consumed any substance on the day of the incident.

Allianz’s forensic scientist concuded the motorist had consumed a cannabis preparation containing THC, misstated his consumption, had a very high level of THC in his blood after the accident which suggested the cannabis had been ingested rather than smoked, was a relatively inexperienced driver and was taking medication, though that had no effect on influence of the cannabis.

AFCA said that report was “thorough, logical and its conclusions are compelling” and also noted a statement from the attending police officer of the motorist appearing “high and under the influence”.

"The panel accepts that it was only an opinion but given the police officer’s independence, the panel is satisfied that it is contemporaneous evidence of being under the influence at the time of the accident,” the ruling said.

This would have impaired the driver's reaction ability, causing or contributing to the loss, it said.

See the full ruling here.