Best-selling author Terry Pratchett marched to Downing Street today to hand in a petition calling for an increase in funding for dementia research.

The former Bristol journalist, who has a rare type of Alzheimer's, will address politicians before handing in the paper with nearly 20,000 names.

Pratchett's campaign on behalf of the Alzheimer's Research Trust has the backing of more than 100 scientists, MPs from all parties, public figures and thousands of members of the public.

The petition to the Prime Minister says: "I am appalled that research into Alzheimer's and related diseases, which affect 700,000 people in the UK, currently receives just 3 per cent of government medical research funding.

"I strongly urge the government to increase funding for dementia research as a matter of urgency."

Earlier this year, Pratchett, who has early onset Alzheimer's, announced a million dollar donation to the charity and is now a patron.

"We are facing, to use the term said to me by one of the leading US researchers, a worldwide tsunami of Alzheimer's and other dementia diseases," he said.

"I intend to scream and harangue while there is time.

"There's only two ways it can go – researchers, with as much help you can give them, may come up with something that reduces the effects of this dreadful, inhuman disease, or we will have to face the consequences of our failure to prevent the final years of many of us being a long bad dream.

"The strain on carers and their support is bad enough now. Before very long the effects on the health service – and society itself – will be unbearable."

The Alzheimer's Research Trust receives no Government funding and has to reject two thirds of grant applications it receives.