African National Congress (ANC) spokesperson Jackson Mthembu was arrested for alleged drunken driving in Cape Town on Thursday morning - but this did not stop him from doing his job.

Mthembu, in a 21-minute telephonic interview with Sapa, apparently while in police custody, passionately defended youth leader Julius Malema before bursting into song.

"Don't blame Julius. In fact, on this one, I will defend him," said Mthembu, speaking on the criminal complaint against Malema for singing "kill the boers, they are rapists".

"You must blame the ANC, don't blame Julius. But when you blame the ANC, then contextualise it," said Mthembu, before he started singing the "kill the boers" song to Sapa over the phone.

Mthembu was arrested on the N2 near the Pinelands off-ramp at 7:50am and was only released from the Mowbray police station after 2pm with a warning that he had to appear in court.

"It is a strange time of day to be under the influence... They had to hold him to allow him to sober up," said JP Smith, Cape Town's mayoral committee member for safety and security.

Sapa phoned him at 9:22am for comment on the Malema story and a 21-minute interview followed. When called back at 11:23am to ask if he had been arrested for drunken driving, Mthembu again answered his phone, but this time the call lasted only 40 seconds. He replied: "I can't comment".

Smith said that normally a person arrested for drunken driving would not have access to his or her cellphone.

"Normally, once they get put in a cell, no, [they don't have access to their cellphones]. But I'm not too perplexed about it. He cooperated with the police at all times, there was no problem from him," said Smith.

The Independent Democrats (ID) called on the ANC to release a statement about Mthembu's arrest.

"Coming so soon after the news that Mthembu apparently sang to a Sapa journalist this morning, the ID regards the reports of his landing up in jail as quite plausible," said ID secretary-general Haniff Hoosen in a statement.

"In fact, seen within the context of the ANC's years-long reputation for saying one thing and doing something completely different, I think it is safe to say that Mr Mthembu has today earned his ANC stripes."

ANC spokesperson Ishmael Mnisi - whose other colleague, Brian Sokutu, was suspended this week - said that party secretary-general Gwede Mantashe was investigating the report of Mthembu's arrest.

"My eardrum is complaining," Mnisi said in jest, when asked how he was doing.

"Mr Mantashe is investigating all those issues [the Mthembu arrest] so we will then take it from there," he added.

Smith said that members of the so-called ghost squad, the city's special unmarked high performance traffic unit, arrested Mthembu.

"Jackson Mthembu was arrested this morning [Thursday] on the N2 for driving in the bus lane. When they pulled him over, there was a strong smell of alcohol and they arrested him," said Smith.

He said that a colleague driving behind Mthembu pulled off the highway and tried to stop the officers from cuffing him. It was only then that the officers realised he was a high-ranking politician, said Smith.

Mthembu was first taken to Mowbray police station. Smith said that a constable at the station did not want to process his case because he was a senior ANC member.

"They were unwilling to process the details against Mthembu. There was a threat made that our officers would be arrested," said Smith.

"The officers felt that they were being intimidated because of the political credentials of the person involved."

The ghost squad members then took him to the Safely Home Anti Drunk-driving Operations War Room (Shadow) in Athlone, after which he was taken back to the Mowbray police station.

"The law should not protect politicians," said Smith.

"He was tested for alcohol and was found to be more than three times over the legal limit. He tested 0,87 while the legal limit is 0,24 [milligrams of alcohol per 1000 millilitres of breath]," Smith said.

He was tested with a breathalyser.

"It's a pretty watertight case," said Smith.

Cape traffic spokesperson Kevin Jacobs confirmed that a senior ANC member was arrested for drunken driving on Thursday morning.

Earlier this week, Sokutu, also an ANC spokesperson, was suspended for remarks he made about President Jacob Zuma failing to declare his financial interests on time.