The amount of money spent on private ambulances in Yorkshire more than tripled between 2010/11 and 2012/13. Figures from freedom of information requests show the cost increased from £500,000 to £1.8m.
Labour has warned of a risk to patient safety saying people would be stunned that "blue-light 999 services" were being privatised without proper debate. He will write to Health Secretary Jeremy Hunt to ask for an urgent assurance about the safety and quality of all privately emergency ambulances.
On Wednesday the House of Lords will debate controversial rules which could open the health service up to more competition.