 There is a duty on Category 1 responders (including the NHS) to make appropriate arrangements for major incidents, and as such private and voluntary ambulance services are generally included as part of local planning for the provision of ambulance services during major incidents, such as mass casualty events (including 7 July 2005 London bombings), adverse weather, or severe staff shortage.Private ambulance services are common in the UK, with over 200 providers, and their use under contract to the NHS to answer 999 calls has been growing year on year, with every NHS ambulance trust using private providers in each year from 2011–2014, and contracted providers answering three-quarters of a million 999 calls in that three-year period.Expenditure on private ambulances in England increased from £37m in 2011–12 to £67.5m in 2013/4, rising in London from £796,000 to more than £8.8m.