Former Tory chief whip Andrew Mitchell continues to deny calling police officers on duty at Downing Street 'plebs' ITN

The Police Federation has expressed "great regret" after Scotland Yard arrested an officer from the diplomatic protection group, SO6, over the alleged leaking of information to the press about an incident at Downing Street in which Andrew Mitchell, the then chief whip, is said to have called officers "plebs".

News of the arrest came as Mitchell said the contents of the alleged police logbook, recording the incident, were false.

The constable from the specialist Metropolitan police unit, which guards embassies as well as members of the government, was bailed on Sunday after his arrest the day before, and has been suspended from duty.

The Met said in a statement on Sunday night that its directorate of professional standards arrested the officer on suspicion of misconduct in a public office after the force received fresh information on Thursday regarding the alleged unauthorised disclosure of information.

Scotland Yard sources indicated on Monday there was no suggestion any payment had been involved in the alleged disclosure of information. But the Met refused to comment on where the fresh information that led to the officer's arrest on Saturday night had come from.

The chairman of the Met Police Federation said it was of great regret that Scotland Yard had taken action against an officer over "plebgate". John Tully said the federation would support members through any difficulties they faced. "Clearly it is of great regret that the MPS has found it necessary to take this action – I trust justice will ultimately prevail," he said.

The row in September developed after police at Downing Street refused to open the main gates to allow Mitchell to take his bicycle through, instead forcing him to use the side gate. Allegations of the words used in the exchange that followed led to the Tory MP resigning as chief whip in October after an unsuccessful month-long fight to fend off the claims and save his career.

The exact words used by the politician on the night have been disputed ever since. Mitchell maintained he "did not use the words attributed to me" and denied using the word pleb, although he has admitted to saying: "I thought you guys were supposed to fucking help us." It has been argued since then that he should have been arrested for abusing a police officer – a public order offence.

On Monday Mitchell told ITV News: "I'd just like to reiterate once again that it's the contents of the alleged police log which are false … they are false and I want to make that very clear."

Weeks before Mitchell's resignation the Met launched an investigation into how the Sun obtained an internal report suggesting Mitchell did call the officers plebs. The tabloid, which broke the original story about the incident, said it had seen a police report of the incident, prepared for senior officers, which indicated that Mitchell also swore repeatedly at officers.

The arrest is the latest in a crackdown by the Met on relationships between the police and the press as a result of the Leveson inquiry. Media guidelines say any officer suspected of leaking information should be subjected to disciplinary and/or criminal investigation.

The Met – and the Association of Chief Police Officers (Acpo) – have welcomed the Leveson report, which recommends police whistleblowers who are acting in the public interest should not go to the media but instead report their concerns internally, to Her Majesty's Inspectorate of Constabulary or to the Independent Police Complaints Commission (IPCC). Andy Trotter, an Acpo spokesman on media relations, has said that most whistleblowers are gossips interested in embarrassing others in their organisation.

Earlier this month the Guardian reported how another constable – James Patrick – was being investigated for gross misconduct for a series of blogs and tweets – which he turned into a book detailing his belief that reform of the police service is putting the public at risk.

Patrick's lawyer, Karen Todner, said he was a whistleblower and the issue was one of freedom of expression. "This is someone who has tried to raise his concerns through the legitimate channels but was not able to do so," said Todner.

In its statement regarding the arrest the Met said it had contacted the IPCC on Sunday and would formally refer the matter to the body on Monday. "The arrest is linked to previous inquiries by the MPS as to how internal MPS information was obtained by national newspapers following an incident at Downing Street in September," it added.

"These inquiries found no evidence to suggest any of the officers involved in the incident were involved in the unauthorised release of information."

At a regular Westminster briefing the prime minister's spokesman said: "At the time we said there was a genuine difference of opinion.

"Clearly this is something the police are dealing with and I don't think I want to get drawn into further comment."

Asked if the prime minister was concerned about the arrest of the whistleblower, the spokesman added: "That arrest is a matter for the Metropolitan police."

Asked whether the arrest was a proportionate response, the deputy prime minister, Nick Clegg, said it would be "so wrong" for politicians to "start jumping in and providing a running commentary".

"It's not for politicians to do at all," he said during questions following a speech. "Obviously this is a controversial issue but I really think it should be left for the police and the prosecuting authorities to make up their own minds."

The former Tory minister David Mellor said it was good news that the police finally seemed to be taking leaks to the media seriously. "What happened in the Mitchell case was a serious breach of duty with not only the full details of police reports being leaked, but the actual documents being handed over to newspapers," he said.

"This was disgraceful. The question has to be asked, what took them so long?"

Mellor said he would be watching with interest to see whether the arrest would be taken further, and whether it would change "deeply ingrained" behaviour among the police.

• This article was amended on 23 December 2012 to clarify a reference to remarks made by Andy Trotter in a previous Guardian article.