Successive scandals over MPs' expenses, banking and phone hacking have shaken people's confidence in Britain "to the core", David Cameron has warned.
The Prime Minister said the public felt that the rich and powerful had been "serving themselves".
From now on institutions would have to be "beyond reproach" in order to win back trust.
The comments, in an interview with the Big Issue, came after Business Secretary Vince Cable insisted Rupert Murdoch's dominance of the UK media landscape had been "deeply unhelpful" and must never be repeated.
Mr Cameron said: "Over the past few years, this country has had some real knocks and people's confidence in our country has been shaken to the core. I'm talking about the expenses scandal, the financial crisis, this whole disgraceful and sorry episode of phone hacking.
"There's a sense that the rich and the powerful - politicians, bankers, the press and the police - have been serving themselves, not each other. Add to all that the way the world is changing, with the rise of new powers like China and India, and I think there's a general feeling that maybe our best days as a country are behind us.
"I passionately believe that is not the case. So if you ask me what I want Britain to look like and feel like at the end of my time as Prime Minister, I want us to be a country - and a people - which has our confidence back. Institutions that are beyond reproach, that serve the public not the other way round."
Mr Cable was stripped of responsibility for deciding the fate of News Corporation's bid for full ownership of BSkyB last year after he was recorded in a newspaper sting saying he was at "war" with Mr Murdoch. The Liberal Democrat minister told the BBC on Sunday there was nothing "personal" about recent concerns raised about the media mogul.
"The balanced historical view would be that he has made positive contributions," he said. "But we are dealing with the world as it actually is, where we have had a very, very dominant media company and we need to deal with the lessons from that."
Mr Cable said it was right that Ofcom should look at whether News Corp's UK subsidiary News International was "fit and proper" to hold a majority stake in BSkyB.