The NHS must spend millions of pounds to fill front-line staffing gaps left by striking doctors.
In one instance, a consultant in Plymouth was paid over £3,000 to cover a junior doctor's 12.5-hour night duty.
Paying for coverage costs hospitals three times as much as the wages deducted from junior physicians on strike, hospitals report.
The finding comes as junior physicians in England join consultants already on strike and walk out again.
It is the first time both junior and senior physicians have gone on strike at the same time, a move that is likely to cause significant disruption.
During the first three junior doctor's strikes, University Hospitals Plymouth spent over £1.8 million for cover, including £1.59 million to consultants. However, the hospital only saved slightly more than £430,000 in wage deductions.
Hull University Hospitals NHS Trust, where three-quarters of junior doctors have been joining picket lines, paid roughly £1.7 million to consultants and other senior doctors providing cover during the first four walkouts.
This is three times the amount that was saved. According to a trust spokeswoman, the organization was required to pay the premium rates that the British Medical Association (BMA) was asking its members to charge.
She stated that they are expected to provide vital services, such as cancer treatment and emergency care, to the residents of the Humber and North Yorkshire region despite the obstacles.
When asked to conduct non-contractual work, the union advises that doctors consult the BMA's rate card, which contains the premium rates. This includes filling in for junior doctors even within their own department when they are unavailable.
The rates for consultants range from as low as £161 an hour for day hours to as high as £269 an hour for night shifts, which is approximately three times what they would typically be paid in accordance with the terms of their contract.
However, trusts are the ones who decide whether or not to pay these rates, and the data provided by the NHS shows that not all trusts are doing so.
Matthew Taylor, the head of the NHS Confederation, which represents hospitals, stated that his members had attempted to fight, but many of them had to give in to keep key services running.
Mr. Taylor stated that they believe trusts will have no choice but to pay inflated prices to ensure patient safety. Mr. Taylor added that planning, preparing, and coping with the aftermath of strikes now consumes one-third of the time of senior managers.
As hospitals' income is dependent on the number of patients seen, canceling treatments incurs additional expenses.
NHS England estimated that the four-day junior doctors' strike in April resulted in more than 200,000 canceled appointments and cost the health service more than £300 million.
Deputy chief executive Saffron Cordery stated that trusts are truly enduring the financial burden of industrial action month after month.
In addition, the mandated premium rates reflected "just how strained industrial relations had become." Ms. Cordery added, "We need the government and unions to settle down and talk to prevent strikes from becoming routine."