More than 60 per cent of dementia sufferers are not known to their GPs, according to research by the Liberal Democrats.
The party’s health spokesman Norman Lamb said the figures showed the need for improved access to primary care.
Researchers compared the Alzheimer’s Society’s estimates of the number of sufferers in each primary care trust area with GP disease registers.
It is predicted that there are 575,000 people in England with dementia, but only 220,000 are known to their GPs.
According to the estimates 95 per cent of primary care trusts have fewer than half of the registered dementia patients expected.
Fifteen PCTs have more than 5,000 sufferers in their area who are not on a GP disease register, according to the analysis.
Ignored and dismissed
Mr Lamb said: “These extraordinary findings beg the question why so many are going without the help their GP can offer.
“People with dementia, their families and carers have the right to expect access to services that help them carry on with their lives. They do not deserve to be ignored and dismissed.
“The NHS must do more to ensure people are encouraged to seek early help when they start having problems and that they have access to care from their GP, specialist assessment and accurate diagnosis.”