The slide in patient satisfaction with practice opening times in the GP Patient Survey 2008, occurred regardless of changes in practice opening hours.
Practice ratings slumped or soared, while opening hours remained unchanged.
Practices offering core hours only were as likely to get top scores as practices offering extended hours, the survey found.
The survey showed a 2 per cent drop in patient satisfaction in England.
Rates dropped or stayed static in every PCT except Barking and Dagenham, where they rose by 1 per cent to reach the national average of 82 per cent.
This year's survey was run between January and March, when the profession was in a contract stand-off with the government and anti-GP media hype was at an all-time high.
In Islington, satisfaction with opening hours slumped by 4 per cent to 77 per cent, although an extended hours LES was introduced in December 2007.
Of three practices that had 99 per cent patient ratings for opening hours, one is open for 20 and a half hours a week.
Dr Alan Bell's practice in Pontefract opens from 8.30-11am on five days and 4-6pm on four days a week.
Patients at Dr Hung Song Kor's single-handed practice in South Shields gave him a 12 per cent boost, bringing his satisfaction rating to 94 per cent - although the practice is only open during core hours.
Dr Rajendra Kumar Rathi's practice in Barrow-in-Furness also opens only in core hours, but patients reported 98 per cent satisfaction with opening hours.
2% drop in patient satisfaction with practice opening times
Source: NHS Information Centre.
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