The staggering increase comes amid major concern in the NHS over the use of temporary staff and associated spiralling costs.
Public service sector union Unison has called for the service to stop using agency staff by October.
Bryn Webster, Unison chairman for Yorkshire Ambulance Service (YAS), said: “We think it is a waste of money and is not necessarily giving the best patient care.”
The figures, which were revealed in a Freedom of Information request, show YAS spent £1,739 on agency paramedics in 2014-15 but that rose to £310,847 in 2015-16. The trust, which does not have a budget for agency staff, also had no expenditure on agency paramedics in 2013-14.
YAS said it had resorted to agency staff due to a national shortage of paramedics, but Mr Webster said while demand for the service had risen the trust needed to develop their existing workforce. The union has added concerns over the governance of agency staff.
He added: “They should invest in the current staff rather than using expensive agency staff.”
York MP Julian Sturdy also said he was concerned by the ‘incredible increase’ in expenditure.
He said: “Since 2010 the Government have been supporting ambulance trusts to train 2,307 new full-time paramedics in England, a 22.9 per cent increase, and 1,900 more will be qualified by 2020. Unfortunately the total number of full-time paramedics in the Yorkshire Ambulance Service has been falling since 2014, whilst numbers have increased nationally year-on-year since 2010.”
A spokesman for Yorkshire Ambulance Service NHS Trust said they were actively recruiting for both paramedics and due-to-qualify paramedics.
He added: “The trust is committed to continuing to provide a safe, responsive and high quality service for our communities.”