African National Congress (ANC) spokesperson Jackson Mthembu has been convicted of drunk driving - at more than three times over the limit - following a plea agreement with prosecutors.

He appeared briefly in Cape Town's Wynberg Magistrate's Court on Wednesday, where he was sentenced to a fine of R12 000, half of which was conditionally suspended for five years.

He also pleaded guilty to a charge of driving in the dedicated bus and taxi lane on Cape Town's N2 freeway on the day of his arrest, for which he was fined R500. His driver's licence will be endorsed.

Mthembu, 51, was represented in court by senior Cape Town advocate Norman Arendse.

Speaking to Sapa afterwards, he apologised to his family, to the ANC and to "all South Africans" for failing to meet their expectations.

"What inspired the guilty plea was that I had done something that was wrong," he said.

"It was a stupid mistake, it was poor judgment on my part. Fortunately no-one lost his life through my poor judgement."

He said that he had made a commitment "not to repeat the wrong that I did", and wanted to throw his weight behind the government's Arrive Alive traffic safety campaign.

"I would really like to appeal to all South Africans as we are approaching the festive season of Easter weekend, not do to the stupid thing I did, not to drive under the influence.

"For the sake of our own families and for the sake of other families and all South Africans, let's not drink and drive."

Mthembu was pulled over by a member of the city's Ghost Squad, an unmarked traffic unit, as he was driving in the bus lane just before 8am on March 11.

According to the plea agreement, the officer suspected that he might be under the influence of alcohol and asked him to accompany her for a breathalyser test.

"The accused cooperated fully," the agreement read.

However, the city claimed that South African Police Service (SAPS) officials at Mowbray police station tried to prevent from him being charged and threatened to arrest the Ghost Squad members. The claims are being investigated by the SAPS provincial office.

Mthembu was released from the Mowbray police station later that day on warning.

The breathalyser gave a result of 0,85mg of alcohol per 1000ml of breath. The legal limit is 0,24.

The plea agreement listed as "general aggravating factors" that it was a serious offence to drive a vehicle "having an excessive amount of alcohol in any specimen of breath".

"The offence is more serious when committed by a person who stands in a position of trust to the public," it said.

Also listed as an aggravating factor was that Mthembu occupied a high-profile public position. Although he was not involved in an accident, he had been a potential threat to other road users, the agreement stated.

In Mthembu's favour, however, was that he was not a young man, that he had pleaded guilty and "expedited the conclusion of the matter", that he had not been involved in any accident, and had cooperated fully from the outset.

"He indicated from the beginning that he was sorry, and he thus showed remorse," the agreement read.

Asked about his future as ANC spokesperson, Mthembu told Sapa that he had apologised to the party's national executive last week, and that apology had been accepted.

He had not received any indication that the leadership was planning any action against him.