Doctors and patients are fighting plans to create a "super surgery" in Oxfordshire.
The Government has asked every Primary Care Trust in England to set up at least one so-called polyclinic - a surgery with up to 25 doctors, offering multiple services 12 hours a day, seven days a week.
But campaigners say it would "threaten the very survival" of smaller practices.
A new clinic is set to be built in Banbury next year, but many of the county's doctors are opposed to the plans.
They claim the centres, which may be privately run, could kill off local surgeries and put profits before patients.
Dr Jo Jenkins, Dr Jon Bickford and Dr Emma Bolton - all of Marston Medical Centre - cycled to the British Medical Association's headquarters in London last week to deliver a 550-name anti-polyclinic petition.
The BMA has sent petitions to every surgery in the country and presented the signatures to 10 Downing Street yesterday.
Dr Jenkins said: "Our patients really value the personal care we provide in a small practice.
"They can walk to us from their home and we value being part of the local community.
"The diversion of funding away from small general practices is threatening our very survival.
"The Department of Health should be investing in existing local services instead of wasting taxpayers' money on huge, impersonal, commercial surgeries."
At East Oxford Health Centre, in Cowley Road, more than 1,000 people signed the BMA petition.
Dr Helen Groom said: "We are fully behind it and against the attack on GPs and the privatisation of the health service.
"Polyclinics are a huge worry for us and for patients.
"Big multi-national companies could be running these clinics and putting profits first."
Paul Roblin, of the Oxfordshire Local Medical Committee, said: "GPs in Oxfordshire believe the funding for the privately owned polyclinic could be better spent on the health needs of Oxfordshire patients.
"For example, the money spent on the clinic could buy more than 1,000 cataract operations or 140 hip operations."
Alan Webb, director of commissioning for Oxfordshire PCT, insisted the new facility would be a GP health centre, not a polyclinic.
He said: "It's an additional service with additional funding and there are absolutely no plans to close any surgeries as a result of this."
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