Boris Johnson was accused of "totally inappropriate" contacts with Rupert Murdoch after it was revealed he attended a private dinner at the media mogul's home.
The London Mayor defied critics again by joining a number of high-profile guests including Homeland actor Damian Lewis at the gathering.
His office said it would not comment on the Mayor's "private engagements" but Johnson has never shied away from admitting close contacts with the News Corporation boss.
He was previously criticised for inviting Murdoch and his wife as Olympic Games guests and the latest encounter prompted claims of a conflict of interest over Scotland Yard investigations involving Murdoch-owned newspapers.
A spokesman for campaign group Hacked Off, which represents some high-profile victims of phone hacking, said: "It beggars belief that anyone could describe a dinner between the most powerful politician in London and the head of News Corporation, the company at the centre of the phone-hacking scandal, as a 'private arrangement'.
"The Mayor is also in charge of the Metropolitan Police Authority and it is totally inappropriate for him to be meeting Murdoch in private while the Met are carrying out an investigation into Murdoch companies.
"We urge all politicians to comply with the Leveson recommendations and publish full and up-to-date accounts of their meetings with media proprietors and editors.
"Given their past record of excessive closeness, and all the harm it has done, that is the very least the public can expect from those who represent them."
Len Duvall, leader of the Labour group at the London Assembly, said: "He is the Mayor of London and has a duty to uphold the highest standards.
"Does he really think meeting for a private dinner with Rupert Murdoch is a normal meeting? What planet does he live on?"