CLAIMS that patients admitted to hospital at weekends are more likely to die than those admitted during the week are based on flawed data, Oxford University researchers have said.

Concerns over the so-called "weekend effect" has been one of the key factors behind the Government's push for a seven-day NHS which has led to the dispute with the junior doctors.

However, research by Oxford University has found that the difference in mortality rates is down to differences in the way deaths are recorded - or "coded".

The lead author, Professor Peter Rothwell, said that if these differences were stripped out, the weekend effect disappeared completely.

The findings echo similar research published last week by the University of Manchester.

Prof Rothwell told the BBC Radio 4 Today programme: "What you'd really need to do to study this - the basic due diligence - would be to make sure that there isn't a difference in the coding of data between the weekend and weekday admissions, but nobody had done that.

"It turns out there are quite big differences between the accuracy of diagnostic coding for weekend admissions versus weekday admissions.

"There are several biases but the main one is that there are a lot of admissions during the week for routine care - for pre-planned rehabilitation after stroke, for example, or investigations which are miscoded subsequently as being acute strokes - and of course those patients have a low mortality during the week and so that gives you the illusion of a higher mortality during the weekend.

"From a clinical point of view we just don't see a problem for emergency admissions at the weekend and the data don't support there being a problem."

A spokesman for NHS England said: "This report about data collection covering one condition from nine GP practices in no way alters the wider issue that sick patients should rightly expect to be seen by a consultant within a few hours, have prompt access to tests and treatments and receive joined-up care, whatever day of the week they fall ill, as recommended by the Academy of Medical Royal Colleges."

Downing Street said there was "clear evidence" from eight linked studies that a higher death rate is connected to lower staffing levels at the weekend.

A spokesman added: "That's the consensus from scientific experts. Those studies said variable staffing levels were likely to be a key factor in the weekend effect.

"This small study isn't suddenly the bottom line on this issue, given the amount of evidence to the contrary."