Different GP performances mean that some patients have to wait longer than others to be referred to a hospital, a report from the King's Fund has revealed.
In addition, some patients have been found to be unnecessarily referred to specialists for further investigation, while others do not get referrals even though they need one.
The report found evidence of late GP referral in some areas, particularly for several types of cancer, although most patients were referred within recommended timeframes.
It said that although most GP care is good there are gaps with wide referral rate and diagnosis variations.
The report, from the King's Fund, said: "An important component of cancer referral relates to the assessment of urgency, and there is a growing evidence base questioning GPs' ability to do this accurately."
The report is based on the findings of an inquiry into general practice launched by the think tank in 2009.