Police investigating the phone hacking scandal must act on the evidence "wherever it leads", David Cameron insisted today in the wake of charges against former News International chief executive Rebekah Brooks.

Asked whether he was upset by the action against Mrs Brooks and her husband Charlie, both friends of the Prime Minister, he said the justice system had to take its "proper course".

Mr and Mrs Brooks and four others were charged this week with conspiracy to pervert the course of justice.

The couple vowed to fight the allegations in court and attacked police and prosecutors over what Mrs Brooks called "an expensive sideshow and a waste of public money".

But the Prime Minister, who has faced criticism over his social engagements with Mrs Brooks, told ITV1's Daybreak: "I think it's very important that the police, the justice authorities, that they follow the evidence wherever it leads and they take all the action.

"They are independent in this country, they don't obey the orders of the Government and that's the way it should be. So that has to take its proper course and its natural course."

Mr Cameron said there were "big lessons to learn from all of this" and suggested that politicians had not tackled issues of media regulation properly in the past because of their closeness to the press.

"I think the broader picture, as I've said before, is the whole relationship between politicians on the one hand, the media on the other, became too close and the danger with that is that the politicians didn't then spend enough time talking about some of the problems, in terms of regulation, with the media that we needed to," he said.

The Prime Minister insisted that the freedom of the press must not be threatened in the fallout from the phone hacking scandal and the Leveson Inquiry into the media.

"This is a problem that's gone on for decades and there's an opportunity to sort it out, but we must do it in a way that protects the freedom of the press," he said.

"I think the press worry about that, and I completely understand that, again I listen to those arguments, I don't cut myself off from that, we want a free vigorous press in this country and that mustn't be threatened."