Many patients are still facing long waits for key diagnostic tests on their bowels or stomachs, despite the drive to cut times, a health watchdog says.
Endoscopes are used for diagnostics
The Healthcare Commission found huge variations in waiting times in a poll of 201 hospitals providing the procedures, known as endoscopies.
In some hospitals in England patients wait over a year, while others are seen within a month, the commission said.
The government said it was looking to address the problems.
Every year just over a million patients in England undergo an endoscopy - an invasive procedure which involves a probe to check for abnormalities such as ulcers or cancer.
The survey found that half of patients in south-east England were waiting more than six months, compared with 0.2% of patients in the north east.
From the end of March, all trusts must ensure diagnostic tests are carried out within 13 weeks of GP referral in a bid to drive down the overall wait for treatment to 18 weeks by next year.
In December last year, when the survey was carried out, a third of patients were waiting longer than that for lower bowel examinations and a fifth for examinations of the upper digestive tract, which includes the stomach and part of the small intestine.
But the watchdog said much progress had been made since a few years ago when waits of over a year were quite common.
The Healthcare Commission urged more to be done to reduce cancellations as many clinics are cancelled because of competing demands on clinicians' time.
It also called for the creation of more space for recovery as bottlenecks can be created by patients recovering from the procedures.
The report also said the quality of patient care needed to be improved as some patients were being over-sedated and signing consent forms before they undressed, which is against NHS guidelines.
Healthcare Commission chief executive Anna Walker said: "It is unacceptable that patients in some parts of the country have to wait so much longer than in other regions."
Jonathan Green, vice president of the British Society of Gastroenterology, said: "Endoscopy is something that has sprung up in a rather ad-hoc way. Hospitals organise it quite differently and that is why there are a lot of variations.
"I think this is because we never had the focus on diagnostics that we do now. But I think things are improving massively."
A spokeswoman for the Department of Health said endoscopy had been identified as a "key area of focus" with a project set up to spread best practice.
"This programme of work will help to achieve the ultimate goal, to improve patient experience."