A veteran policeman has branded a man, caught steering his car with his knees while holding a mobile phone in each hand, as one of the most careless drivers he has ever seen.

Acting Sergeant Rob Atkinson was in an unmarked police car when he noticed a city-bound Honda swerving in the far-left lane of the Eastlink tunnel about 3.15pm on Saturday.

As he pulled up beside the 30-year-old Fitzroy man, acting Sergeant Atkinson was stunned to see he was driving with one finger on the steering wheel as he held a phone in each hand.

Once out of the tunnel, the driver was pulled over and told police he had been transferring information from one phone to the other while gripping the wheel with his finger.

Acting Sergeant Atkinson said that, in 10 years on the force, the incident was one of the worst cases of careless driving he had seen.

The man was fined just over $500 and was penalised six demerit points.

"I reinforced the danger of this type of driving, especially within the tunnel and issued the man with two penalty notices," acting Sergeant Atkinson said.