text: The NHS spent £8.84m on private ambulances in the capital last year compared to £795,000 in 2011, according to Freedom of Information data.
  The London Ambulance Service (LAS) conceded it was losing staff due to "pressure on the organisation".
  But LAS denied claims it had employed private staff previously sacked by the NHS.
  Heidi Alexander, Labour MP for Lewisham East, claimed London ambulances were taking "on average two minutes longer than three years ago" to respond to the most serious call-outs.
  Labour said its research discovered private ambulance usage by ambulance trusts across the country grew by 82% between financial years 2011/12 and 2013/14, from £37m to £67.5m last year.
  Private ambulance spending In Yorkshire and the North East more than quadrupled to hit £3.56m and £2.9m respectively, said Labour, although other ambulance services maintained low spending during the two years, while one trust reduced its reliance on private vehicles.
  Shadow health minister Jamie Reed raised concerns over the figures and the "increasing use" of private ambulances during health questions in the House of Commons.
  But his comments were branded "absolute nonsense" by public health minister Jane Ellison, who said that previous Labour government "occasionally deployed private ambulances too".
  Brendan Kemp, regional organiser for the GMB union, questioned the hiring practices of ambulance trusts and their ability to keep staff.
  "Who's checking the qualifications of the staff that man these vehicles?" he said on BBC London 94.9.
  "Often staff that have been dismissed by London Ambulance Service for something, often they'll reappear working for a private contractor."
  But Jason Killens, director of operations for the LAS, said every private contractor "is checked by us before we use them".
  "Staff that leave the LAS for reasons of clinical safety would not be redeployed on those private contracts with us," he told BBC London 94.9.
  Mr Killens said increasing demand each year "is adding pressure in the organisation" and conceded that "some staff leave" as a result, with about 500 vacancies currently unfilled.
  He added: "There is a small number that leave us and go and work in the private sector, but the vast majority of people that leave the ambulance service in London go to work elsewhere in the NHS."
target: Spending on private ambulances in London grew by 1,000% between 2011 and 2013, the Labour party has claimed.