Doctors' surgeries in Dartford, Gravesham and Swanley have thousands of patients on their registers who may be dead or have left the area, according to analysis of NHS figures.

So-called ghost patients are a serious problem for the NHS, as the money allocated to surgeries is linked to the number of patients on their books.

The most recent estimate for the population of Dartford, Gravesham and Swanley CCG, which is in charge of commissioning healthcare services in the area, is 260,643 - but there were 270,384 patients registered with GP surgeries in the area last month.

This means up to 9,740 of these could be ghost patients, or 3.6% of all those registered.

The Office for National Statistics last updated its population estimates in mid 2016, so it is possible that population growth may account for some ghost patients.

But analysis of ONS figures shows that, between 2011 and 2016, the population grew by 1.1% on average each year, so it is unlikely this accounts for all extra patients.

GP surgeries receive funding based on the number of people they have registered, which is then weighted to take into account key patient demographics like gender, age and disability.

Dartford, Gravesham and Swanley CCG was allocated £35.74 million from the NHS based on the number of registered patients in the 2016-2017 financial year. NHS figures show this was an average amount per patient of £132.28.

The funding formula is revised annually but based on these figures, the CCG would receive around £35.77 million for patients on the register in the coming financial year. But if the population figure was used instead of the patient register it would be £34.48 million.

This means as much as £1.3 million would be allocated to ghost patients.

The health service has found no evidence that doctors are deliberately inflating patient numbers, and blames poor record keeping for the number of ghost patients.

As far back as 2012, the Audit Commission identified this problem with GPs' record keeping and removed 95,000 patients from surgeries' lists.

But the problem appears to be getting worse. Three years ago, there were up to -26 ghost patients in Dartford, Gravesham and Swanley, compared to 9,741 in the latest figures.

There will be more ghost patients in areas with high student populations, according to research published by the House of Commons Library. It's also possible that in some places, particularly those with high numbers of short term migrants, the Office for National Statistics may have underestimated the resident population.

The NHS has been concerned about ghost patients for some time, and in 2016, it hired private company Capita to clear non-existent patients from GPs' registers. The firm has written to patients who have not contacted their registered practice within five years, as this could be an indicator that the patient has moved away.

NHS England says it factors ghost patients into its budget allocations. A spokesman said: “GP practices work hard to keep their registered patient lists as accurate as possible and NHS England is working with Capita and GP surgeries to transform this process, make it digital and any savings identified will be ploughed back into the NHS.”