From the birth of the NHS in 1948, private medicine has continued to exist, paid for partly by private insurance. Provision of private healthcare acquired by means of private health insurance, funded as part of an employer funded healthcare scheme or paid directly by the customer, though provision can be restricted for those with conditions such as AIDS/HIV. In recent years, despite some evidence that a large proportion of the public oppose such involvement, the private sector has been used to increase NHS capacity. In addition, there is some relatively minor sector crossover between public and private provision with it possible for some NHS patients to be treated in private healthcare facilities and some NHS facilities let out to the private sector for privately funded treatments or for pre- and post-operative care. However, since private hospitals tend to manage only routine operations and lack a level 3 critical care unit (or intensive therapy unit), unexpected emergencies may lead to the patient being transferred to an NHS hospital.