The number of people waiting for NHS treatment may be twice the figures being reported, with millions missing from official data, the Telegraph has learned.
Analysis seen by this paper shows that the current method of counting vastly underestimates the true scale of the problem, with some patients lost in the system or removed before treatment is complete.
Latest official figures show that a record 6.4 million patients were waiting for treatment in March, one in 10 of the population, an increase of three per cent since February.
But the Telegraph understands the true figure may be closer to 13 million, almost one in five people in Britain.
Insiders have warned that hospitals are being incentivised to bring patients in for a first appointment and get them off the waiting list quickly, even though they may still require many months of treatment or operations.
The NHS considers a patient removed from the waiting list once they are seen following a Referral for Treatment (RTT), usually from a GP. Yet if they cannot make that appointment, some trusts are automatically removing them from the waiting lists.
Experts also warned that the RTT definition is so loose that an appointment with a consultant who decided to keep a health condition under surveillance could also count as treatment – knocking a patient off the waiting list – even if they required further help later.
The clock also stops with the first course of treatment – meaning that a patient given painkillers for a knee complaint, could be counted as “treated” despite facing a wait of many years for surgery to address the real problem.
One source working in waiting list management said follow-up lists were “at least twice as large” as the reported backlog.
“The big political risk is people getting sight of these numbers,” she said.
“The published numbers focus on Referral to Treatment, but there are millions more follow-on appointments which are essentially invisible, as far as the headline national reports go.
“Once you’ve had that first treatment the upshot is that you just don’t exist in NHS waiting terms, as far as the national records go.”
Targets for seeing patients within 18 weeks are also based on the public waitlist figures, and so do not include those still waiting for treatment after an initial appointment.
Sajid Javid has previously warned that the waiting list could rise to 13 million, meaning the true figure could rise far higher once “hidden waiters” are factored in.
Analysts also warned that NHS waiting list data was littered with errors, such as duplicate entries and dead patients, with some estimates suggesting that 15 per cent of the information could be inaccurate.
Clunky and antiquated computer systems are also leaving patients on the waiting lists of dead or retired consultants, or scheduling operations for when surgeons and anaesthetists are on holiday or double-booked elsewhere, it emerged.
Robert Ede, head of health and care at Policy Exchange, said it was impossible to estimate the true waiting list because of the bureaucratic chaos.
“The data is a complete mess,” he said. “One NHS trust looking at it found 15 per cent of the information was completely incorrect – patients who are duplicates, or errors or in some cases, dead.”
The Telegraph also discovered that some hospitals are cancelling entire morning or afternoon theatre sessions if only a handful of patients are booked in, to keep their utilisation rates high.
And analysts found that some patients were missing entirely from waiting lists
“It’s cancer patients and they were still waiting, and they always would have been waiting,” a source told the Telegraph. “It’s really scary.”
The NHS has now sent in private data teams to uncover the scale of the problem, and streamline systems to bring down the backlog. A recent push on “data cleaning” may explain why growth in waiting lists almost halted in the run-up to Christmas, as inaccurate cases were taken off the lists.
In some trusts, analysts were able to cut waiting lists by a third through simple interventions such as merging staff holiday rotas and theatre diaries, removing dead patients, and using real-time information about consultant or bed availability.
Analysts discovered that many trusts were unaware of their true backlog figure, with clinicians, managers, executives and schedulers all working to a different number.
Experts said many NHS trusts were wary of “pulling back the curtain” as it could show a far worse position than is known about.