Dr John Hughes, a general practitioner from Manchester, said the Government's care reform is a "good idea in theory", but in practice it is totally "unworkable".
He said: "We're seeing twice as many patients as we were six years ago so we are all working to capacity and I'm not sure these proposals will make any difference at all, if anything they may actually worsen waiting times."
"If people have an individual GP that GP has other work to do as well", he added, "we can't be there 24/7 365 days a year, it's simply not physically possible."
Jeremy Hunt will say that every patient should have a doctor who is responsible for their care 24/7 when he announces reforms to GP service.
A&Es are getting 'closer to the cliff edge' as ITV News has learned the Health Secretary is to unveil major reforms of Out of Hours care.