Record waiting lists for operations could fuel a rise in negligence claims against the NHS, the National Audit Office has warned.

More than 4.2 million patients are now on waiting lists for surgery, a 55 per cent rise in five years.

The number waiting more than 18 weeks for operations has tripled over the same period, with 528,000 patients forced to wait longer, as key NHS targets have been repeatedly missed.

The NAO report warns: “Given that 40 per cent of clinical negligence claims are brought because of delays in diagnosis or treatment, there is a risk that longer waiting times may lead to an increasing number of future claims.”

The watchdog said long waits were being exacerbated by shortages of staff and beds.

It also warned that a doubling in referrals for suspected cancer in recent years is adding to pressures on services, with 1.94 million urgent referrals in 2017/18, up from 1 million in 2010/11.

One in four patients given an urgent referral now waits at least two months for treatment, official figures show.

The NAO said NHS England’s policy of encouraging more urgent referrals in a bid to improve early cancer diagnosis was likely to explain the trend. A new long-term plan for the NHS pledges to ensure that three quarters of cases are diagnosed