Michael Summers, chairman of the Patients Association, said the plans 'could be beneficial to patients, because out-of-hours services are so appalling.
'But it seems a bit gimmicky,' he added.
Mr Summers said that patients would want reassurance that they could see local GPs, rather than locums brought in from elsewhere.
He also raised questions about the security of patient records.
'There isn't an IT system run by any government department that seems to work, so security will have to be very tight indeed,' he said.
Last month Asda became the second supermarket to announce plans to offer extended hours GP appointments.
The company will run two pilot schemes at stores at Hounslow, west London, and Boston, Lincolnshire. From later this year, GPs will offer appointments at the stores on Saturday mornings and some evenings.
Asda's plans follow the launch of an extended hours service at the Sainsbury's in Heaton Park, Greater Manchester.
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