The London Metropolitan Police (MET) Commissioner Paul Stephenson has resigned.

The surprising move comes on the heels of the phone hacking scandal, where Stephenson, who is Britain's most senior police officer, has faced criticism for hiring former News of the World executive Neil Wallis as an adviser.

Wallis has been questioned by police investigating the hacking.

BBC reports Monday that Stephenson has also faced questions over his stay with his wife at a luxury health spa – Champneys, which employed Wallis as a PR at the time the police chief recuperated from surgery there earlier this year.

The MET acknowledged Stephenson had stayed there for free, but insisted he had been unaware that Wallis had worked as Champneys' PR consultant, pointing out the free stay had been recorded in the senior officer's gifts and hospitality register, due to be published shortly.

The police commissioner says he had no knowledge of the extent of the phone hacking.

"I have taken this decision as a consequence of the ongoing speculation and accusations relating to the MET's links with News International at a senior level and in particular in relation to Mr Neil Wallis. Let me state clearly, I and the people who know me, know that my integrity is completely intact. I may wish we had done some things differently, but I will not lose sleep over my personal integrity," Stephenson said in a statement.

He explained he had informed Buckingham Palace and his employer, London Mayor Boris Johnson, about his decision to resign.

Stephenson hired Wallis as a PR consultant for the MET from October 2009 until September last year. Wallis was paid GBP 24 000 to work as a two-day-a-month PR. The contract was cancelled four months before the launch of the Operation Weeting investigation into phone hacking began in January this year.

Prime Minister David Cameron, is quoted by BBC, saying "Sir Paul had enjoyed a long and distinguished career in the police."

Ex-News International chief executive Rebekah Brooks was arrested on Sunday by police investigating phone hacking and bribery at the News of the World. After being held for 12 hours, Brooks was released on bail at midnight.