A new report has claimed that almost 600,000 people will have undiagnosed dementia a decade from now.
Current Alzheimer’s Society figures show that there are now just over 300,000 undiagnosed dementia cases.
But the charity says that the next 10 years will see that number almost double, because people are living for longer.
It is thought that by 2021 more than a million people will have the condition.
If nothing is done to improve diagnosis rates, which currently stand at 40%, some 595,725 will be undiagnosed, according to the charity, which has published a map on variations in diagnosis.
Dorset has the lowest rates of diagnosis in the UK - with only a quarter (26%) of those with the condition knowing they have it, rising to 69% in Belfast.
If diagnosis rates stay the same, Milton Keynes will have the biggest gap between people expected to be living with dementia and those who receive a diagnosis.
Belfast is predicted to have the smallest diagnosis gap.
Milton Keynes is the fastest growing area and can expect a 56% increase in people living with the condition, the map also shows.
In contrast, Barking and Dagenham is predicted to have slightly fewer people living with dementia in 2021 than now.
The map is based on prevalence rates for dementia from experts at King’s College London, which have been updated by the charity, alongside information held by GPs.