Cancer is more difficult to treat in its later stages
Failure to pick up cancer at an early stage costs the lives of up to 10,000 a year in England, the government's cancer tsar says.
National Cancer Director Professor Mike Richards described the situation as "unacceptable".
Currently, 90% of patients are diagnosed by symptoms, rather than through screening.
Professor Richards' comments will feature in a forthcoming article in the British Journal of Cancer.
In the piece, Professor Richards says: "These delays in the patient presenting with symptoms and cancer being diagnosed at a late stage inevitably costs lives.
"The situation is unacceptable so the first big step has been to understand why the delays occur."
Professor Richards said that if diagnosis in England was as good as in the best-performing European countries many lives could be saved.
He cited a new study which found about half the deaths that could be prevented were due to Britain's three biggest cancer killers - tumours of the lung, colon and breast.
Professor Richards said part of the problem was that British people were worried about wasting doctors' time, and so often did not present until their symptoms were relatively advanced.
A recent survey by the charity Cancer Research UK found 40% of people would delay visiting a GP for fear of being labelled a time-waster.
Professor Richards said research was now under way to examine how best to tackle this issue.
His staff are working with GPs to carry out a national audit revealing the extent of delays and where they exist.
The National Awareness and Early Diagnosis Initiative (NAEDI) has also been set up to improve screening services.
GPs 'more alert'
Professor Steve Field, chairman of the Royal College of GPs, said GPs should reflect on whether there were things they could do to make sure cancer symptoms were picked up earlier.
He said: "It's wrong to blame GPs for all these deaths, as there are many factors involved, including patients not recognising symptoms of cancer and not talking to their GP about them, especially middle-aged men.
"But I'm sure that we could all at times be more alert to symptoms and investigate and refer patients quicker."
Katherine Murphy, director of the Patients' Association, said: "Some patients are diagnosed with cancer when they have presented with the same symptoms six months earlier.
"Patients will sometimes tell us that they had been going to see their GP for six to nine months with, say, a pain in their stomach and were told to go to the pharmacy and buy an over-the-counter medicine (and later are found to have cancer)."