NHS organisations across England are paying agency staff "hugely inflated" hourly rates to cover gaps in normal cover, the Tories have claimed.
Figures obtained under the Freedom of Information Act also showed that some agencies were taking large "cuts" in return for supplying workers to the NHS.
After requests from the Conservative Party, more than 70% of NHS trusts provided details of the highest amount they paid to an agency worker between May and October 2008.
Dorset Primary Care Trust (PCT) paid £158 an hour for a prison GP, equivalent to an annual salary of £307,000, while NHS Wakefield District PCT paid £135 an hour for a prison GP – equivalent to an annual salary of £263,000.
The figures showed that trusts also paid high sums for nonclinical staff, with Tower Hamlets PCT having paid £157 an hour for a senior manager – equivalent to an annual salary of £306,000 – and Wandsworth PCT handing more than £147 an hour for a strategic commissioning manager.
The size of the cuts taken by agencies were also cause for concern, the Tories said. Somerset Partnership NHS Foundation Trust paid £116 per hour for a nurse but the agency took £50 (43%), while Oxfordshire PCT paid £94 per hour for a nurse with the agency taking £40 (43%).