The Prime Minister's plans to deliver seven-day GP services have been dealt a blow after an official review found there was "very low" demand for Sunday appointments.
Patients also snubbed appointments on Saturday afternoons, although Saturday mornings and weekday evenings proved more popular.
The review examined data from 20 pilot sites across England - covering 1,100 general practices and 7.5 million patients - that have been testing seven-day services.
It comes after David Cameron pledged a "truly seven-day NHS" for patients in accessing GPs, a plan that was described by Downing Street earlier this month as "groundbreaking".
The new report, from independent consultancy firm Mott MacDonald, found there has been some success with the scheme, including better use of weekday GP time.
But it said there had been low up-take of weekend appointments compared with weekday ones, particularly on Sundays.
As a result, some sites have cut their weekend appointments to just a few hours, while others have ceased to offer any extended hours appointments.
The report said: "This pattern of low demand on Sundays has been evident nationwide.
"There are exceptions (for example, Bury, Morecambe and South Kent Coast do not report any utilisation problems at weekends) but the vast majority of pilots have highlighted this in their feedback.
"Often these pilots are reporting that low take-up on Sundays and some (although far fewer) also highlighting low demand on Saturday afternoons and evenings.
"For example, across Darlington, local analysis of its pre-bookable appointments between October 2014 and March 2015 identified that on a Saturday 54% of appointments were booked compared to 12% on a Sunday.
"As a result of Sunday trends, many pilots have begun reducing their weekend service offer to fewer hours, with some ceasing provision on Sundays completely (Watford, Hambleton, Richmondshire and Whitby, Darlington) or are monitoring the situation with a view to potential discontinuation (BHR, Brighton and Hove, Warrington)."
The report said there is "general agreement" that the lack of success with weekend extended hours is not down to how services are communicated to patients, but "rather it is a result of entrenched patient behaviours."
The report said that the "average utilisation" of available appointments during normal core working hours was 94%, dropping to 75% during extended working hours.
It concluded: "Given reported low utilisation on Sundays in most locations, additional hours are most likely to be well utilised if provided during the week or on Saturdays (particularly Saturday mornings).
"Furthermore, where pilots do choose to make some appointment hours available at the weekend, evidence to date suggests that these might best be reserved for urgent care rather than pre-bookable slots."
Video appointments with GPs also did not "prove popular" with patients in some areas, while doctors in some regions were reluctant to offer more phone consultations, preferring to see patients face-to-face.
The Royal College of GPs said the findings came as no surprise and patients "have better things to do on a Sunday afternoon than have their ears syringed".