Health secretary Jeremy Hunt's plans for a seven-day NHS have taken a hit from a Public Accounts Committee report blasting the government for driving forward the plan without having a cost structure in place for it.

"It beggars belief that such a major policy should be advanced with so flimsy a notion of how it will be funded - namely from money earmarked to cover all additional spending in the NHS to the end of the decade," said Meg Hillier MP, chair of the Public Accounts Committee.

A Committee inquiry on the management of clinical staff in the health service concludes that the government and its arms-length bodies have failed to get a grip on the situation, and that "no coherent attempt" has been made to assess headcount implications of major policy initiatives such as the seven-day NHS.

It says the government's commitment to provide an extra £10 billion in funding for the NHS by 2020 is a pot the Department of Health "seems to expect will cover everything - despite not having separately costed seven-day services and other initiatives", and warns: "We are therefore far from convinced that the Department has any assurance that the increase in funding will be sufficient to meet all of its policy objectives".

The current status quo already seems pretty dire: according to the PAC, in 2014 there was an overall shortfall of around 5.9 percent between the number of clinical staff healthcare providers said they needed and the number in post, equating to a gap of around 50,000.

NHS trusts and foundation trusts have been given mixed messages by the government, being set unrealistic efficiency targets on the one hand and ordered to increase staff levels on the other. This has spurred "overly optimistic and aggressive staffing profiles" that have created shortfalls, the Committee noted, and also warned that current efforts to retain clinical staff "are not well managed" which could magnify the problem.

The undersupply of staff prevents trusts from being able to provide services efficiently and effectively, and could potentially increase waiting times and shortcomings in the quality of care, it said, and called on national bodies "to get a better grip on the supply of clinical staff in order to address current and future workforce pressures".

The report comes just days after Oxford researchers concluded that claims that patients admitted to hospital at weekends are more likely to die than those admitted during the week are based on flawed data, finding that the difference in mortality rates is actually down to differences in the way deaths are "coded".

"At a time when there is growing evidence casting doubt on a 'weekend effect' - the basis for the government's plans for expanding seven-day services - this report further underlines the government's failure to consider how it will staff and fund additional services when the NHS is struggling to provide existing services," said Dr Mark Porter, chair of the British Medical Association.

"Despite what ministers claim, NHS funding has not kept up with rising patient demand and the increased cost of delivering care. Staff shortages are seen across the NHS, patients are waiting longer for appointments, and there is no real solution to the £22bn funding gap facing our health service," he noted.