Almost 2,000 people in south Bucks may be living with undiagnosed dementia, according to estimates by the NHS.

Figures collected by GPs show that there are 2,957 people over 65 in the south of the county who have been diagnosed with some form of dementia.

However estimates by the NHS, based on the age profile and gender of the patients, suggest the real figure may be 4,737.

This means an estimated 1,780 patients may be living with the debilitating illness that has not been formally recorded by their doctor.

Statistics suggest a staggering 961 people in Wycombe may be living with undiagnosed dementia, compared with 458 in the Chiltern District and 361 in South Bucks.

The figures are being collected in response to the Prime Minister's Challenge on Dementia set up by the previous PM, David Cameron.

The Department of Health wants GP surgeries in England to increase the rate of diagnosis. The target was for at least two thirds of the estimated number of people with dementia to be diagnosed by March 2015. The latest data, for April this year, shows that the diagnosis rate for the whole of England is 67.3% but area to area this ranges from 41% to 90%.

The Royal College of General Practitioners said that doctors realised the importance of spotting the signs of dementia early but in some circumstances might delay making a formal diagnosis in the interests of patients and due to pressure on services to support them.

Professor Helen Stokes-Lampard, Chair of the RCGP, said: "There may be some situations where GPs might validly consider it in the best interest of the patient to delay seeking a formal diagnosis, especially in the early stages of the condition if there is minimal adverse effect on daily living and functioning and where patients do not want to be labelled.

"This decision might also be influenced by GPs knowledge of the local availability of assessment and treatment services, which may be insufficient to meet demand."

Dementia is a term used to describe symptoms such as loss of memory, behaviour changes and problems in reasoning. The most common cause of dementia is Alzheimer's disease, which accounts for about 60% of cases, but it can be the result of brain damage caused by a stroke or neurological conditions such as Parkinson's.

The Alzheimer's Society said that getting a diagnosis allows people with dementia to access emotional, practical, legal and financial advice, as well as any support and treatment available.

The society's senior policy officer, Andrew Boaden, said: "Dementia diagnosis rates vary significantly from place to place, which is concerning.

"With the number of people with dementia set to reach 1 million by 2021, the Government and the NHS must do more to address this issue."