Junior doctors have entered a second day of strike action as the bitter dispute over pay shows no sign of being resolved.

Health Secretary Steve Barclay said the timing of the strike was “regrettable” and he accused the British Medical Association (BMA) of putting patients at “greater risk” after not agreeing any national exemptions for strike action for some services, such as cancer care.

Elsewhere, the BMA released a statement amid reports that one of its junior doctors committee co-chairmen, Dr Robert Laurenson, was on holiday during the strikes.

“Dr Laurenson is off work this week fulfilling a long-standing commitment to attend the wedding of a family friend,” a spokesperson said.

“We aren’t going to disclose further personal information but he remains actively involved in the planning of the dispute.”

The Government and the union appeared to be deadlocked after Downing Street insisted there will be no talks unless junior doctors abandon their starting position of a 35% rise and call off the strikes.

It comes as hospital bosses expressed concern about keeping patients safe as they struggle to secure cover for overnight junior doctor shifts during strikes.

NHS Providers warned that the 96-hour walkout will cause a “very long, difficult week” for the health service.

And the health service’s top doctor warned that the situation in the NHS will “become more challenging each day this strike progresses”.

NHS England’s national medical director Professor Sir Stephen Powis said: “Staff are working incredibly hard during this unprecedented period of industrial action, and we expect the situation to become more challenging each day this strike progresses.

“As the week goes on, we expect to see staff cover stretched as those who worked tirelessly over the Easter holiday take leave, which will pose a huge challenge to an already depleted workforce.”

Meanwhile, some doctors at a hospital in Weston-Super-Mare have been asked to return to work due to patient safety fears.

Under NHS contingency plans, hospital leaders can request for doctors to return to work for a limited time in certain circumstances “to maintain safe patient care”.

The BMA said on Tuesday: “Protecting patient safety during strikes has always been a priority to the BMA. However, poor planning by local management has left the Emergency Department and acute medicine at Weston General Hospital exposed.

“As a result, the BMA has agreed that a total of seven junior doctors can be asked to volunteer to return to work today and tomorrow.”

Miriam Deakin, director of policy and strategy at NHS Providers, which represents NHS trusts, said: “Keeping patients as safe as possible, trusts’ number one priority, will be even harder than in previous strikes, so it’s all hands on deck.

“Trust leaders are worried about securing adequate cover for the night shifts ahead.

“This is going to be a very long, difficult week for the NHS.”

Due to the timing of the strike, a number of senior doctors are unable to provide cover as they did in the previous three-day strike.

Mr Barclay said: “I deeply regret these strikes and in particular the timing, which been timed deliberately coming straight after Easter, the fact that the BMA junior doctors have asked their members not to tell NHS managers whether they intended to go on strike or not – making contingency planning more difficult – and also their refusal to agree on any national exemptions.

“Other health unions like the Royal College of Nursing agreed national exemptions, particularly, for example, for cancer patients so that those patients weren’t impacted.

“The junior doctors committee has refused any national exemptions and obviously that puts patients at greater risk, but we’re working very hard to mitigate those impacts.

“We are ready to have discussions with them but clearly a demand for 35% – over £20,000 for some junior doctors – is not fair or reasonable.”

Dr Vivek Trivedi, co-chairman of the BMA’s junior doctors committee, told the PA news agency: “We just want them to come to the table in an honest and meaningful way.

“The Government has not even tried to meet us anywhere in the middle, it hasn’t given us a counter-offer at all.”

It has been estimated that some 350,000 appointments and operations have been rescheduled as a result of the action.

The BMA has claimed junior doctors in England have seen a 26% real-terms pay cut since 2008/09 because pay rises have been below inflation.

It has asked for a full pay restoration that the Government said would amount to a 35% pay rise – which ministers have said is unaffordable.

The union said junior doctors can earn as little as £14.09 per hour in their basic pay packet.