Negotiations over doctors' pension reforms could reopen today after GPs and hospital doctors staged their first industrial action in almost 40 years.
The British Medical Association (BMA) said it was willing to get back round the table with the Government following yesterday's action.
Dr Hamish Meldrum, chairman of council at the BMA, said doctors have sent a "strong message" to ministers that a better deal on pensions must be found.
Figures showed the action hit almost a fifth of GP practices.
In some areas of England, 26% of GP surgeries would see only those patients in urgent need of care.
Across the country, 2,703 operations were postponed and 18,717 outpatient appointments were rescheduled, based on figures from strategic health authorities in England.
The data suggests the action affected services at 21% of GP practices across the country.
In the south of England, 482 practices, or 26%, saw at least one member of staff take action while in the Midlands and the East of England a quarter of GP surgeries operated a reduced service.
In the north of England, 23% of GP surgeries took part in the day of action and 11% of practices in London treated only urgent cases.
Meanwhile, the Department of Health claimed just 8% of doctors working in the NHS in England, or 11,500, showed their support.
The BMA announced the day of action last month after it accused ministers of pressing ahead with "totally unjustified" increases in pension contributions and a later retirement age for doctors, even though a deal on pensions was agreed four years ago.
The union postponed all non-urgent work and added that although the action will be disruptive, doctors will ensure patient safety is protected.
Mr Meldrum said: "Because doctors have been in their places of work as usual, it was always going to be difficult to put a figure on the number taking part - the Government's figures need to be treated with extreme caution.
"Our feedback from the doctors co-ordinating the action on the ground indicates that in England up to a quarter of non-urgent cases have been postponed, and around a third of GP practices have been taking some form of action.
"Our intention has not been to maximise the impact on patients, but to communicate the scale of doctors' anger and to encourage the Government back to the table.
"Doctors have sent a strong message that a fairer approach must be found."
Yesterday, Mr Meldrum told ITV's Daybreak: "I hope that after today we can sit down and we can talk.
"Nobody wants more of this, nobody wants a repeat of this. I'm not out to inconvenience patients because of this. Our fight is not with patients it is with the Government."
Health Secretary Andrew Lansley said: "In the run up to these strikes our objective has been to minimise disruption for patients.
"We asked doctors to recognise that their quarrel was not with patients but with the Government.
"I am pleased that a significant majority of doctors have done just that and maintained services for their patients.
"It is extremely regrettable if any patients have suffered unnecessarily. We will do everything we can to ensure that those patients get their treatment as soon as possible. I call on the BMA to commit to further co-operation to enable patients to have their rescheduled operations and appointments as soon as possible."
The last time doctors took action was in 1975, when consultants suspended goodwill activities and worked to contract over a contractual dispute, and junior doctors worked to a 40-hour week because of dissatisfaction with the progress of contract negotiations.
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