Alan Johnson, the Health Secretary, has sent a letter to every GP in England asking them to open their surgeries in the evenings and at weekends.

Mr Johnson's letter indicates that funding claimed by the practices could be cut if they hold out in the row between the Government and the British Medical Association (BMA).

The BMA yesterday accused ministers of bullying and said the practices stood to lose an average of £36,000 under the changes outlined in the letter.

The association says it is willing to have surgeries open for an extra two hours on average – the equivalent of 6.30pm to 8.30pm on a weekday, or a short Saturday morning surgery.

But the Government is proposing that surgeries open for an extra half an hour for every 1,000 patients on their books. This would mean an extra three hours per week for an average-sized GP practice with 6,000 patients.

In his letter, Mr Johnson said the proposals "do not in any way reduce the substantial existing investment in these areas, and this sort of care is at the very heart of general practice".

Ministers want GPs' hours in England to be extended in line with other European countries.