The man who drove his old Mercedes-Benz past the Woodlands Checkpoint on Saturday managed to do so because a security barrier meant to stop unauthorised cars from leaving the checkpoint was ineffective.

It was the first time the barrier failed to stop a car, said the Immigration and Checkpoints Authority (ICA) on Sunday.

On Saturday, the man, a 65-year-old Malaysian national, who is also a Singapore permanent resident, drove the Singapore-registered car through the checkpoint at 4.05pm after he was stopped for a boot check.

He bolted from the checkpoint and evaded the authorities for more than five hours, before he was arrested by the police at 9.15pm.

The security barrier, installed in 2006, was about knee height and designed to puncture the tyres of vehicles that try to drive over it. It is checked daily and on Saturday punctured one of the tyres of the car, but did not stop it in its tracks. The ICA is investigating why the barrier was ineffective.

The failure of the security barrier drew a sharp rebuke from Deputy Prime Minister Teo Chee Hean on Sunday: "The alarm and barrier systems at the checkpoints are inadequate, and they need to be improved and strengthened considerably."

Mr Teo, who is also the Home Affairs Minister overseeing the ICA, added: "I have directed the commissioner of the ICA to implement measures to better secure our checkpoints as soon as possible."

The police revealed on Sunday that the man is also under probe for drug offences, saying that a packet suspected to contain drugs was found when the man was arrested.

But the police would not be drawn into giving details of how the drugs were found, or how these were connected to the checkpoint breach on Saturday.

They also declined to explain why the manhunt took longer than five hours, only saying that they had devoted extensive resources for the search and the man was determined to give police the slip, through methods including abandoning the car.

The man is likely to be charged in court tomorrow.