The Telegraph's investigation shows how revenue at one of the NHS’s largest outsourced recruitment firms, Independent Clinical Services (ICS), increased by 60 per cent in just two years, to £314 million.
Meanwhile, spending on agency staff by NHS foundation trusts – two-thirds of hospitals – rose by 64 per cent over a two-year period, pushing the health service into debt.
Figures obtained by The Telegraph show that Barts Health NHS Trust in London spent most heavily on agency staff, with an £81 million bill in 2014-15.
It was followed by King’s College Hospital foundation trust and Royal Free London NHS trust, which each spent more than £60 million.
The trusts blame their reliance on temporary staff on a lack of qualified nurses. Many have tried to employ more nurses in the wake of the Mid Staffs scandal, but struggled to find permanent workers, causing the agency bill to spiral.