The number of people with dementia who endure the “frightening isolation” of living alone will double to 240,000 over the next 20 years, an Alzheimer’s charity has predicted.

They experience a crushing loneliness after suffering a loss of friends and social contact, compounded by public “awkwardness” about dealing with people with dementia, according to the Alzheimer’s Society.

Jeremy Hughes, the charity’s chief executive, said: “Too many people face a future alone with dementia and without adequate support. Dementia shouldn’t mean becoming a prisoner in your own home.

“The frightening isolation of so many people with dementia is a wake-up call for all of us. It shouldn’t mean that everyday activities, like going to the local shop, fill you with anxiety and dread.” He added that too many people with dementia end up feeling “abandoned and isolated, with nowhere to turn”.

When the charity surveyed 354 people with dementia, 58% said they experienced loneliness and 56% said they suffered from isolation. The same number (56%) said they had been losing touch with people since being diagnosed.

Ernie Malt, who has vascular dementia, told the charity: “I do get lonely. I have family, but they’re not nearby, and it’s not very often that people come to see me at home.

“When you live alone it’s the little things that cause you problems, like walking into the kitchen and not knowing why you’re there, or trying to do something on the computer but not having a clue what your password is.”

A sizeable minority (33%) of dementia patients have become emotionally distant from their friends since their diagnosis, while 24% say some of their friends do not know about it.

The number of people with dementia in the UK living on their own would rise from 120,000 to about 240,000 by 2039, the Alzheimer’s Society estimated.

Similarly, it predicted that the number of people with dementia living in their local community and not in a care home would reach 700,000 by 2025 and then climb to 1.3 million by 2051 – the equivalent of the population of Birmingham. That is according to its new projections, which are based on analysis of ONS and other official data.

The number of people overall with dementia in the UK was expected to increase from 850,000 to 1 million by 2021 and then again to 2 million by 2051 as a result of people living longer.

Separate recent YouGov polling among adults for the charity found that many people feel awkward or nervous about interacting with people with dementia, with 40% saying they would not feel confident about communicating with them, while 26% said they would feel nervous.