A 13-year-old boy driving at almost 140km/h while his father slept in the passenger seat tried to fool police into thinking he was his older brother - but he couldn't spell his name.

Police say the boy lacked the cognitive skills to drive and the incident was "a disaster waiting to happen".

An attack of gout is being blamed for the father relinquishing the wheel to his young son, as the pair were driving home to Huntly from a school camp on Friday afternoon.

Their Honda sedan was pulled over by a highway patrol officer on State Highway 1B near Taupiri in the Waikato about 1.45pm.

The boy tried to give his older brother's name, but when he spelt it incorrectly police became suspicious and he eventually came clean.

The father told police his son had been driving because he was suffering from gout - a disease caused by a build-up of uric acid in the blood, and marked by sudden and painful attacks.

Waikato road policing manager Leo Tooman said the man's foot did appear to be swollen - a common symptom of the ailment.

The officer made the father drive the rest of the way home.

The incident was "a disaster waiting to happen", Mr Tooman said.

"Most 13-year-olds simply don't have the cognitive skills to take in the big picture - this is totally unacceptable behaviour."

The man has been charged with aiding and abetting an unlicensed driver and will appear in the Huntly District Court this week. His son has been referred to youth aid.

"The father may feel he's woken up from a bad dream now that he's facing charges," Mr Tooman said.

"But imagine the potential nightmare that could have occurred if they'd crashed at that speed."