Most women who could benefit from a powerful breast cancer drug are not receiving it, a survey suggests.
Herceptin is cleared for use by the NHS
Studies show Herceptin can help women diagnosed with a particularly aggressive form of the disease.
The government's drug watchdog, the National Institute for Clinical Excellence, says that the NHS should pay for the drug.
However, the survey, carried out by makers Roche, found that only a third of suitable patients were getting it.
The Department of Health does not collect information about how many women are prescribed Herceptin, which can extend lifespan - and improve quality of life - among women with advanced breast cancer.
The NICE decision was expected to cost the NHS £17 million a year, but charity CancerBacup said there remained a "postcode lottery" in which some areas supplied the drug freely, while in neighbouring communities, it was not readily available.
In some areas the problem is particularly bad - in the Midlands only 14% of eligible women get the drug, compared with 28% in the north of England, 33.5% in south-west England and 61% in the south-east.
In all the figures suggest that as many as 1,000 women with breast cancer were being unfairly denied the drug.
CancerBacup chief executive Joanne Rule said that all health authorities and local hospital trusts should be monitored, and forced to comply with NICE guidance.
She said: "It's daft that the only way that the NHS knows what's being prescribed is if the manufacturers tell them."
Herceptin is only suitable for women who have a certain gene - HER2 - and it is often the lack of testing facilities locally which obstructs them from receiving the drug.
Unless a HER2 test has been carried out, then the drug cannot be given.
Ian Gibson MP, the chairman ofthe All-Party Parliamentary Group on Cancer, said: "It's time for the government to get rough and tough with cancer service providers.
"People deserve to have all the facts at their fingertips."
Health minister Melanie Johnson that the NHS had to fund treatments which had been given the thumbs-up by NICE.
She said: "We are committed to ending the postcode lottery so that patients who need vital drugs are not denied them on the grounds of funding.
"I have asked strategic health authorities to look closely at this new evidence and raise it at a local level with the trusts that provide services.
"Patients should be getting the drugs they need and we will do all we can to resolve the problem."
Delyth Morgan, chief executive of Breakthrough Breast Cancer said: "Breakthrough campaigned hard to ensure NICE the approved herceptin, a drug which can give extra precious months of life to an estimated 3,000 women with advanced breast cancer.
"We believe women should be offered the best available care whoever they are and wherever they live.
"While effort is put into researching and developing improved, life-enhancing treatments like herceptin - equal effort is needed to ensure they reach the patients they are intended for, otherwise, what is the point?"