Late diagnosis of cancer means that between 5,000 and 10,000 people a year are dying who might otherwise have survived, according to National Cancer director Professor Mike Richards.
The government's cancer-services chief says that the delays "inevitably costs lives. The situation is unacceptable, so the first big step has been to understand why the delays occur".
His comments, made at a time of growing concern about the quality of UK health care, are to be published in a forthcoming edition of the British Journal of Cancer.
A study has shown that Britain's three biggest cancer killers are lung (34,589 deaths in 2007) colon (16,087) and breast (12,082).
Prof Richards says that they comprise about half of all the deaths that could have been avoided if diagnosis was as good as the best-performing European countries.
He says: "Research is already under way to investigate the best ways to break down any barriers between GPs and patients and how to reduce delays in primary care."
His staff are working with GPs to carry out a national audit revealing the extent of delays, and where they exist.
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British Journal of Cancer