Peers describe David Cameron's intervention in case ' after Kate McCann's open letter to Sun ' as PR exercise

The PM has been accused of bowing to the Murdoch empire over his decision to intervene in the Madeleine McCann case. Photograph: Carl Court/AFP/Getty Images

Two peers who are members of police watchdogs warned that the independence of the Metropolitan police was under threat after the prime minister brought in Scotland Yard to review the disappearance of Madeleine McCann.

Insiders at the Yard played down any suggestions that their role could quickly lead to any breakthrough in the case, saying that the review, which will cost millions of pounds, could take months or even years.

Labour's Lord Harris, a member of the Metropolitan Police Authority, accused David Cameron of bowing to Rupert Murdoch's empire, referring to Cameron's decision to call in Scotland Yard after Kate McCann wrote an open letter in the Sun asking for his help.

Lord Bradshaw, the Liberal Democrat peer and vice-chairman of Thames Valley Police Authority, added his voice to the criticism, describing the prime minister's intervention as a PR exercise. "I am mightily worried about the politicisation of the police force. What appears on the face of it to be fairly innocuous orders ' it's a fairly short step from there to telling the police they have got to investigate this rather than that," Bradshaw said.

Harris said: "This ... is entirely predictable in terms of the 'pulling power' of News International on Government policy ... However, his [Cameron's] intervention drives a coach and horses through the draft protocol issued by the Home Office designed to preserve the operational independence of the police."

Writing on his blog, the peer added: "I can imagine that the senior leadership of the Metropolitan police are not exactly happy about this. It again embroils their officers in a high-profile investigation, where the chances of success are unclear, and which will divert limited investigative resources away from other matters."

In a statement Scotland Yard denied it had been ordered to review the abduction. It said that the commissioner, Sir Paul Stephenson, received a request which he considered and decided on balance that it was the best course to take.

Kerry Needham, the mother of Ben Needham, the British toddler who was abducted on Crete 20 years ago, said: "I am pleased for the McCann family and look forward to the government offering the same support to all the families with children missing abroad."

If the Yard is given access to all the Portuguese documentation the first task will be to have it translated. As part of the review the Met's team ' likely to be led by a detective chief inspector within the homicide command ' will also examine files held by Leicestershire police, the McCanns' home force, who gave some help to the Portuguese officers. There is also documentation from a number of private investigators hired by the McCanns over the last four years.

Although there was irritation among senior figures at Scotland Yard at being bounced into an inquiry, one source predicted that it would be quickly overtaken by a desire to do the best job possible. "It was political. But at the end of the day a child is missing."

The Met has a copy of a review into Madeleine's disappearance completed by Jim Gamble, when he was head of Ceop, the child exploitation and online protection centre. It is understood to recommend that Scotland Yard be brought in to work with the Portuguese police on a review, but his report has been sitting on the home secretary's desk for more than a year until this week with no action taken.

Scotland Yard released the letter to Sir Paul from Theresa May on Thursday. In it the home secretary says diplomatic contact has been made with the Portuguese police, who have indicated they would co-operate with Scotland Yard. But she made clear it would be down to the Yard to negotiate the details.

The McCanns repeated their thanks to Cameron, saying the Met's involvement was a positive step.