Britain's top police officer, Sir Paul Stephenson, who is under fire for hiring the former News of the World deputy editor Neil Wallis as his PR adviser, reportedly accepted 20 nights free of charge at the luxury health spa Champneys earlier this year.

The revelations, published on the front page of the Sunday Times, will pile further pressure on the Metropolitan police commissioner, who has been under attack since he admitted employing Wallis on a fee of £1,000 a day, just hours after the former News International executive's arrest last week in connection with the phone-hacking inquiry.

The revelations are particularly damaging for Stephenson because Wallis, known to his Fleet Street colleagues as "the Wolfman", was also retained by Champneys to manage its public relations. A spokesperson for the Met said the commissioner was unaware of Wallis's connection with the Hertfordshire spa when he accepted its hospitality.

Stephenson and his wife stayed on full board over a five-week period while he recuperated from hospital treatment. In a statement, the Met said the meals and accommodation, estimated to have been worth around £12,000, were arranged and paid for by the spa's managing director Stephen Purdew. The statement describes Purdew as a "personal family friend".

"Following his operations, the commissioner stayed with his wife at Champneys Medical from Monday to Friday over a period of five weeks earlier this year where he underwent an extensive programme of hydro- and physiotherapy. This enabled him to return to work six weeks earlier than anticipated. As with many officers, the Met paid the intensive physiotherapy costs."

The commissioner's stay will be declared in the Met's hospitality register, due to be published shortly.

The London Assembly chair Jeanette Arnold, a member of the Metropolitan Police Authority, which supervises the force, said she was "flabbergasted". "Yesterday the confidence was low, today my confidence in him is completely shattered," she said.

Stephenson has also come under pressure to resign over his handling of the hacking scandal and his decision to hire Wallis. The Labour MP Chris Bryant tweeted on Saturday evening: "I am firmly convinced now that the Metropolitan police was corrupted to its core by NI [News International]. Stephenson and [John] Yates have to go." Yates conducted the 2009 review of the police investigation into hacking at News of the World and concluded that it did not need to be reopened.