Patricia Hewitt, the Secretary of State for Health, announced the move, expected to cost £100m a year, after criticism that life-saving drugs are being denied because of delays in the official approval process. Herceptin is available on the NHS only for women with advanced breast cancer, despite evidence that it can be effective for those diagnosed early. It is administered nine to 12 months after diagnosis, surgery and chemotherapy.

On Monday, Barbara Clark, a nurse with early-stage breast cancer, succeeded in her campaign to be treated with Herceptin by her local NHS trust. The same day, a report showed Britain has one of the worst records in Europe for treating people with cancer.

But starting today, all women diagnosed with early-stage breast cancer will be tested to see if their tumours carry a protein called HER2, which indicates whether a patient may benefit from Herceptin. The Department of Health estimates 5,000 of the 35,000 women diagnosed with breast cancer each year in the UK could be treated.

Roche, the company that makes Herceptin, has not yet applied for a licence for its use in early-stage breast cancer because it is still amassing the huge amount of data required by the authorities. It is expected to submit an application next February and receive a licence by July.

The National Institute for Health and Clinical Excellence (Nice), the body that makes recommendations on NHS prescribing, has taken the unusual step of starting its appraisal process of Herceptin before the licence application. It means the drug should be available on the NHS as soon as a licence is approved. Nice has been criticised for taking too long to assess and approve new treatments. Yesterday's decision means women who are tested this week should receive the drug as soon as they need it. Ms Hewitt said: "Herceptin has the potential to save many women's lives and I want to see it in widespread use on the NHS.

"I want the licence for Herceptin to be granted as quickly as possible, without compromising people's safety, and to be available within weeks of the licence being given. I share the huge frustration of many women about the delays in getting Herceptin licensed. I am determined to take action, and this represents a major step forward in our fight against cancer."

But women who have already been diagnosed with breast cancer will not automatically be tested for HER2 and may not have access to Herceptin, although they can appeal to their local NHS trust. Professor John Toy, medical director of Cancer Research UK, said: "Time is of the essence when treating cancer patients, so it is essential new treatments be made available as quickly as possible."