It said on Monday it would consider industrial action in the form of a work-to-rule if need be.

But ministers have decided to push on with the plan, arguing they have provided enough financial support to allow GP practices to introduce the new measure.

Many practices have already been offering this option for years - although some do turn it off during busy periods.

Currently, around 6 million appointments a month are booked online - about one in five of the total.

Care Minister Stephen Kinnock said: "We promised to tackle the 8am scramble and make it easier for patients to access their GP practice - and that's exactly what we're delivering.

"We are bringing our analogue health service into the digital era, giving patients greater choice and convenience. We've learned from GPs who are already offering this service and reaping the rewards."

This is the second major digital announcement this week after the prime minister unveiled plans for NHS Online - a virtual hospital service - at the Labour Party conference on Tuesday.

Digital innovation was one of the core themes of the 10-year NHS plan unveiled over the summer.

The government said it had invested an extra £1.1 billion to support this move.

The government has argued online GP booking will help free up phone lines for those who need to get through to a doctor urgently, as well as relieving pressure on A&E units. Research show that when patients struggle to get through to their GP on the phone they are more likely to turn to A&E.

Currently just over half of patients report that it is easy to get through on the phone, according to NHS England's GP patient survey.

The government said the change was agreed with the BMA back in April as part of the reforms the government made to the GP contract.

Dr Amanda Doyle, of NHS England, said: "This step will help modernise general practice by making online access as easy as calling or walking in to your practice, ensuring the phone lines are available for those who need them most and making it easier for practices to triage patients based on clinical need."

And Jacob Lant, chief executive of the patient watchdog National Voices, said: "Online booking systems are a fundamental building block of a 21st Century NHS, but until now implementation has been frustratingly patchy.

"The best GP practices have shown what's possible. It is true that primary care is under immense pressure, but the answer to managing demand has to be in using these digital systems more effectively."

Practices are also now being required to publish on their websites a new patient charter dubbed "You and Your GP" - informing patients what they can expect from their practice and how to give feedback or raise concerns.

Every GP practice must now offer online booking