Fantasy novelist Terry Pratchett, Columbo star Peter Falk and former Prime Minister Lady Thatcher are all believed to be suffering with the condition.

It affects around 700,000 people in the UK and is expected to increase more than threefold in the next 50 years.

Yet dementia is still regarded as one of the "last great taboos".

The condition results in a slow deterioration of the mind that leads to sufferers losing treasured memories and forgetting loved ones.

In Bristol alone, about 6,000 people have dementia and over the next 20 years this is expected to rise by 33 per cent.

But the stigma surrounding it means that only one in three sufferers ever get a formal diagnosis and others have no idea where to turn for help.

Now a new campaign aims to change all that.

Local Councils, NHS Primary Care Trusts, the Strategic Health Authority for the South West and the Alzheimer's Society, supported by the Evening Post, are looking at how dementia services can be improved.

Richard Lyle, programme director for older people, Bristol City Council/NHS Bristol, said: "The launch of the National Dementia Strategy is extremely welcome in Bristol. It is bringing to the forefront a condition that affects thousands of people across the city. We will be working very closely with all our partners to ensure that the strategy is implemented at a local level, and that people with dementia and their carers receive the best possible care."

Helen England Co-Director of Commissioning, NHS Bristol said: "We are committed to working with partners to ensure that people with dementia and their carers are able to access the best possible care when they need it. Supporting people in the early stages of dementia is vital, and we are delighted that a group of GP practices are able to access a dementia support officer, which has been commissioned in partnership with the Alzheimer's Society.

"They want to raise awareness of the condition, dispel the myths surrounding it and look at how sufferers and their carers can get the vital support they need."

Neil Hunt, chief executive of the Alzheimer's Society, said: "We are dealing with one of the last great taboos here.

"There can barely be a family in the land which has not been touched by dementia at some stage.

"The most important thing we can do is to reduce some of the stigma and some of the myths.

"We are doing a lot to try and dispel those feelings of doom and despair that surrounds dementia. It is nothing like the death sentence that people fear it is. Looking at the services we provide is not just about looking at how we can care for these people, but also what we can do to maximise their potential."

Earlier this year, the Department for Health launched the first ever National Dementia Strategy for England.

Backed by £150 million over the first two years, it sets out plans to increase awareness of dementia, ensure early diagnosis and intervention, and improve the quality of care given to people with dementia.

It has called for a national public information campaign to improve public awareness about dementia and reduce the stigma of the disease.

Jenny Owen, president of the Association of Directors of Adult Social Services (ADASS), co-chaired the dementia strategy and found many people felt as though they were left in the dark.

She said: "People could see it was a growing problem and it was a horrible illness but didn't know that there was anything they could do about it. It was difficult to think about anything positively.

"Making the public aware that dementia is an illness and not just a simple product of growing old is really important.

"People were saying that they really valued getting information from people who could signpost them – like doctors and health professionals – but also from each other.

"They were getting a lot of support from other people who had dementia.

"I think the most important aspect of this campaign will be to hear from people with dementia and their carers – not just from those people who come in through the doors of their GP or their health centre."

David Johnstone, chairman of the ADASS performance and standards network, said: "A lot of people aren't aware of dementia but it is something that is increasingly affecting a lot of people. People with dementia and their carers can be very isolated. Carers have to spend a huge amount of time looking after them.

"As we have an ageing population, many more people will be affected by it. It is about reaching out to people with dementia and their carers.

"We want to show them there is a network of carer services and health services being built up."

He added: "The other aspect of this campaign which is very important is that we do want to find out from people what it is that they have found particularly valuable when coping with dementia. We want to find out how good we are at the moment and what are the gaps between what we are doing and what we need to be doing.

"We are quite excited about this. This might prove to be a really interesting way for the health services to connect and raise awareness and get information back from people who are not part of the normal system."