A health watchdog warned yesterday it would "hold the NHS's feet to the fire" as it identified 47 trusts that were failing to provide an acceptable service to patients.

The Care Quality Commission said annual performance ratings for every NHS trust in England, published today, showed 20 were rated "weak" on quality and a further 27 had never been rated better than "fair" on either quality or financial management in the four years since the present assessment system began. One trust, the Royal Cornwall in Treliske, had been rated weak on quality for four years in a row. Three others had been rated weak for three years in a row.

Cynthia Bower, chairwoman of the Commission, said all NHS trusts will require a licence to operate under new legal requirements being introduced next April, and the 47 trusts identified faced a tough challenge to meet the necessary standards.

"A number of organisations have been underperforming for too long. They must do better for their patients. I want to ring alarm bells in the boardrooms of these organisations. We are committed to improving the persistent underperformers. We will hold the NHS's feet to the fire," she said.

Ms Bower said in the past the commission and its predecessors had been limited to identifying trusts with problems and leaving it to local health authorities to sort out. From next April, the commission will acquire new powers to impose sanctions on failing trusts, ranging from issuing warning notices to imposing conditions on their registration, fines or other penalties, or even prosecution.

She said sacking managers had proved ineffective. "A number of trusts like the Royal Cornwall have had successive managements – that is clearly not a solution. We are going to work with trusts to get to the source of the problem. We are going to be insistent."

A Department of Health spokesman said: "This is the most rigorous assessment of standards the NHS has ever seen. For the small number of Trusts whose performance is weak, we expect immediate action to be taken to remedy this quickly and to prepare for registration with the CQC next year. Earlier this year we introduced a tough new performance regime and will not hesitate to trigger this if we need to.”