London CNN  —  Tens of thousands of nurses and nearly 12,000 ambulance workers went on strike Monday over pay and working conditions in the biggest walkout in the 75-year history of Britain’s National Health Service (NHS). Escalating industrial action comes after years of falling wages, stretched budgets and staff shortages that have left the NHS in a state of crisis, with waiting times for treatment at a record high. At the same time, an aging population needs its services more than ever. That unhappy mix is fueling a boom in demand for private health care from a much broader swathe of the UK population than ever before — a fundamental…