Two GP surgeries are opening in Hounslow and Feltham this month.
The practices, at the Heart of Hounslow, Bath Road, Hounslow, and The Centre, Feltham High Street, will open on April 30, and third surgery is scheduled to open in Brentford during September.
The practice in Hounslow will be the first in the borough to welcome patients every day of the year, from 8am to 8pm. It will include a walk-in service for advice and the treatment of minor illnesses and injuries.
When the surgery at the Heart of Hounslow opens, the centre will become one of London's first polyclinics.
The so-called 'super surgeries', offering a range of medical services under one roof, are a key part of the Government's health reforms.
However, many GPs are concerned they will spell the death of local surgeries and make it harder for elderly and disabled patients to access treatment.
Cranford doctor Alick Munro, chairman of the Hounslow Local Medical Committee, claimed the new polyclinic would make life harder for other practices in the area.
"This practice will have the unfair advantage of being sponsored to provide walk-in services at the weekend and that will put increasing pressure on other surgeries," he said.
"I believe, as do many other GPs, that the walk-in service should have been separate from any existing surgery."
Dr Munro added that ministers had 'overestimated' the demand for out-of-hours services, with existing weekend facilities mainly used by unemployed patients.
However, NHS Hounslow chief executive Nick Relph said the longer opening hours would offer residents greater choice and allow them to organise appointments around their busy lifestyles.
"Offering routine access to a GP for 12 hours every day of the year at a town centre location should reduce the need for patients to use hospital accident and emergency facilities for illnesses they would normally see their GP for," he added.
"We see this new service complementing the GP care that already exists in Hounslow by giving patients additional access to care at times when surgeries may be closed or difficult to access."