LONDON — Andrew Mitchell, former chief whip of the U.K.’s ruling Conservative Party, said that elements within London’s Metropolitan Police conducted a “smear campaign” against him that led to his resignation.

Mitchell quit his government role in October after the Sun newspaper reported he abused police guards, calling them “plebs” when they refused to let him cycle through the main gate of Downing Street. Writing in the Sunday Times today, Mitchell said he never used the term and that he told Prime Minister David Cameron that he had not used the “awful toxic language” attributed to him.

“Suddenly I realized I was being stitched up,” he wrote. “I knew it was false but I didn’t know what to do.”

Two people were arrested last week in an investigation of the matter by the police. A report by Channel 4 News on Dec. 18 said a police officer had posed as a member of the public and falsely claimed to have witnessed the events, in an e-mail to his lawmaker.

The sender of the e-mail “is a serving police officer and member of the diplomatic protection squad,” Mitchell said today. Some members of the police force have conducted “a smear campaign against me in pursuit of their own particular agenda,” he said.

Metropolitan Police Commissioner Bernard Hogan-Howe, Britain’s most senior police officer, has curtailed his Christmas break to return to London, the Sunday Times reported, without saying where it got the information.