The Government's plan for a seven-day NHS will be put at risk due to lack of consultants, a doctors' leader has warned.
Professor Jane Dacre, president of the Royal College of Physicians (RCP) accused ministers of pushing out "misleading" figures on the numbers of doctors working in the NHS.
Professor Dacre said data showed that 40% of consultant posts advertised in 2014 stayed vacant owing to a lack of applicants.
She added consultants had told the college "over and over again" that, to be able to provide the best possible care for patients at night and at weekends, there was a need for "many other services" to also be in place at those times.
These include more healthcare staff such as nurses, radiographers and therapists, access to diagnostic and pharmacy services and access to social care services so that patients ready to leave hospital can do so.
In her speech to the RCP's annual conference in Harrogate, Prof Dacre directly addressed Health Secretary Jeremy Hunt's drive for a seven-day NHS.
She insisted there was "no lack of support for a seven-day service from physicians involved in the care of very sick patients", adding: "Our surveys show repeated support for this and over two-thirds of physicians already work across seven days.
"I quote from an email I received last Saturday from a consultant physician: 'I am on today, and am mid-ward round of 83 patients with one junior colleague... I may be at work Jeremy, but we need more people to be in work too'."
She said one in 10 consultants had also had to "act down" to fill vacant trainee posts.
"Even I was given the opportunity to do just that instead of being here," she said.
"Last week I had a genuine email from a locum agency asking me very nicely if I could work three 12-hour shifts as a senior house officer (SHO) in acute medicine on the Isle of Wight. How desperate is that?
"But seriously, so my first big question for the Secretary of State is - if the president of the Royal College of Physicians is being asked to cover SHO posts 70 miles away, if we have neither enough trainees nor consultants to run the service now, how are we going to implement a safe seven-day service?"
A report from the RCP in February showed that 40% of advertised consultant appointments across the UK in 2014 could not be filled.
Prof Dacre said: "If 40% of teaching or policing posts were unfilled, this would be a national crisis... but somehow we doctors are expected to roll our sleeves up and to muddle on through and fill in the gaps ourselves."
She said evidence showed that it was clear that a consultant-led service provides the best service for patients, who fare better with more consultants on the wards.
In a jibe at Mr Hunt, who has come under fire for his use of death rate statistics for patients admitted at weekends, she said: "We, as doctors, unlike politicians, understand statistics.
"We do not confuse association with causation, and we need to continue to investigate what it is about consultant presence that makes the difference.
"But, so far, we hear precious little about how the other support services are to be expanded or reorganised to give us the support we need.
"My worry, and that of other professional groups, is that the squeeze on the junior doctors is only the beginning, and our other clinical colleagues are next in line."
Prof Dacre also used her speech to call for more funds, just a day before Chancellor George Osborne delivers his Budget.
She said: "In 2013, the UK's overall spending on healthcare was 8.5% of GDP, against an EU average of 9%.
"However, countries like France, Germany and Sweden were spending 11% of their GDP on healthcare."