LONDON - Former British prime minister Boris Johnson committed a "clear and unambiguous" breach of rules when he took up a job as a newspaper columnist this month, an ethics body said, calling for reform of a system it said was outdated and ineffective.

Johnson, 58, was named as a Daily Mail columnist this month, returning to a journalism career that had seen him write for several leading British titles, including one that sacked him for making up a quote.

Ministers and civil servants who leave office are required to consult an ethics body, the Advisory Committee on Business Appointments (ACOBA), before taking up new jobs.

The committee had already said Johnson had breached the rules by failing to give it proper notice.

It went further on Tuesday, calling the breach "unambiguous" and saying it showed the need for reform because current rules only offer guidance and lack clarity in areas such as sanctions.

"They were designed to offer guidance when 'good chaps' could be relied on to observe the letter and the spirit of the Rules," ACOBA Chair Eric Pickles said in a letter to the government.

"If it ever existed, that time has long passed and the contemporary world has outgrown the Rules."

It is up to the government to decide what sanctions, if any, Johnson would face for the breach. Johnson's spokesman declined to comment.

Prime Minister Rishi Sunak's spokesman said: "There is work underway in the Cabinet Office, working with Lord Pickles, to improve the operation and efficacy of the rules."

Johnson resigned as a lawmaker earlier this month having seen the findings of a report that concluded that he deliberately misled parliament over rule-breaking parties during COVID lockdowns.

In his broader criticism of the existing system, Pickles also said new areas of corruption were not monitored because they weren't envisaged when the rules were created.

"I am concerned that if the government waits until these reforms can all be implemented together, it risks further scandal in the meantime," Pickles, a former minister, said.

(Reporting by Sachin Ravikumar, additional reporting by Elizabeth Piper; editing by William James)