The study, by statistics firm Dr Foster, showed that people who need to recover in hospital at the weekend fare worse than those who have an operation earlier in the week.

Patients admitted at the weekend are also 3.9% more likely to be readmitted in an emergency and, overall, have a 20% higher chance of dying on weekends.

The findings come as NHS medical director Professor Sir Bruce Keogh prepares to publish his report on seven-day working in the NHS.

Several high-profile studies in recent years have shown that patients admitted to hospital on weekends and bank holidays have poorer outcomes and are more likely to die than those admitted on weekdays.

One problem repeatedly highlighted is the lack of senior staff working on NHS wards at weekends.

Today’s report said that, while weekend care appears to be improving, there are still variations and a lack of access to diagnostic tests.

The number of emergency MRI scans carried out on weekends is 42% lower than during the week, while emergency endoscopies also drop 40%.

Overall, the study says patients are less likely to receive treatment on weekends and are less likely to have an emergency operation within a day or two of being admitted.

People who have suffered a broken hip or fracture also have to wait longer for it to be repaired than somebody admitted during the week.

A poll of more than 5,500 doctors for doctors.net.uk, included in the study, showed that 68% of doctors believe patients admitted on weekends receive poorer care.

This includes 66% of consultants, 76% of middle-grade doctors and 74% of junior doctors.

Eight NHS trusts in today’s report have higher death rates at the weekend than weekdays. These include Colchester Hospital University NHS Foundation Trust and United Lincolnshire Hospitals NHS Trust.

Seven trusts, including East Kent Hospitals University NHS Foundation Trust and University Hospital of North Staffordshire NHS Trust, have patients admitted at the weekend who are more likely to return to hospital after being discharged.

Five trusts, including Bradford Teaching Hospitals NHS Foundation Trust, have longer waiting times for patients needing hip repairs over the weekend.

Eight trusts that have been found to have very low death rates for both weekdays and weekends include North West London Hospitals NHS Trust and Guy’s and St Thomas’ NHS Foundation Trust.

Six have low re-admission rates for weekdays and weekends, and nine have records of a quick repair of broken hips on both weekdays and weekends.

Dr Foster director of research Roger Taylor said: “We have now looked at many different aspects of quality of care. Every indicator we look at shows that patients who come to hospitals on weekends get worse care and worse outcomes.

“We are pleased that the NHS has made addressing this issue a priority and there is evidence that these efforts are already starting to yield benefits for patients with shorter waits for operations at weekends and, in some cases, lower mortality rates.”