Three-quarters of GP practices are "bursting at the seams" and will soon be unsuitable for care, a survey says.
Many GPs say their surgeries are already unsuitable
Doctors said they did not have enough space to add any more services, with one surgery reporting it had used the staff room to administer vaccinations.
GPs said the snapshot poll of 251 surgeries by the British Medical Association cast doubt on plans to move care from hospitals to the community.
But ministers said the findings did not present the full picture.
At the beginning of the year, the government unveiled plans to invest more in community NHS services in England.
They said GPs in the future would provide a whole range of extra services such as diabetes clinics and minor surgeries.
But doctors from across the UK told the BMA that the NHS's 11,000 practices risked not filling their potential because of a lack of funding.
Dr Hamish Meldrum, chairman of the GPC, said: "Despite all the fine talk by ministers of money for new buildings, the fact remains that general practice is bursting at the seams.
"The survey results paint a picture of surgeries where every conceivable space has been converted for clinical use, with consulting rooms in former storage areas and doctors doing their paperwork in the kitchen."
Some 73% felt their surgeries would not be big enough in the future.
Just under 60% said their rooms were already unsuitable for their needs.
Two-thirds of practices said their clinical staff "hot-desked", or moved around different rooms.
And over a third of practices said they had been unable to make the necessary adjustments to comply with the Disability Discrimination Act.
One GP wrote: "We all hot-desk... on Friday we used the staff common room for flu vaccinations."
Another said: "No clinician has their own room. I have had to move desks up to five times in a two-hour period."
And one practice reported: "There are days when there are not enough rooms to allow all the doctors to consult. The extra doctor sits in the kitchen/typing room and works through mail."
Dr Meldrum said most family practices would provide more services and take on extra GPs, nurses and other health professionals if they could extend or improve their premises.
He said: "Minor surgery, physiotherapy, dermatology, counselling, taking blood for tests and treating minor injuries are just some of the extra things practices would like to offer their patients if they had the room."
Health Minister Lord Warner said: "The BMA sample is small. They surveyed only 251 - how can this be a valid basis for such claims?"
He said the government was making money available for new health centres, rather than spending money on existing out-dated practices.
"We don't believe patients should be satisfied with Changing-Room-style makeovers of GP practices."
Andy Kerr, the health minister in Scotland said: "This UK survey only covers 35 out of 1050 Scottish Practice, and simply doesn't reflect the facts on the ground in Scotland.
"Primary care is at the heart of our new health agenda, and we are investing to match that policy."