Two in five pensioners consider their television set to be their main form of company, a charity has warned.
Age UK said that loneliness is a "huge issue" in Britain after a poll found that one in 10 people over the age of 65 often or always feel lonely.
One in eight said they felt cut off from society and 30% said they would like to go out more often.
Of the 2,000 UK adults surveyed, 37% said their TV is their main form of company.
The charity is calling on members of the public to send donations so it can reach more lonely older people through its services.
It warned that extreme loneliness can increase an older person's chance of dying prematurely.
"At Age UK we know how devastating loneliness can be for older people and these figures are another reminder of the scale of this issue," said Age UK's charity director Caroline Abrahams.
"Loneliness not only makes life miserable for older people, it is also really bad for their health making them more vulnerable to illness and disease.
"It is time to take loneliness seriously and that's why we're asking everyone to take action by donating today to help us carry on supporting older people to make the most out of later life.
"Voluntary sector services like Age UK's have never been more important because funding cuts are forcing many of the local services that help older people stay connected, such as lunch clubs, to scale down or close."
Kate Jopling, director for the Campaign to End Loneliness, added: "It should be a grave concern to health and social care managers that so many older people are now severely lonely.
"The evidence is clear that loneliness leads to avoidable ill health. If we fail to take this public health issue seriously now we may end up pushing already stretched services to breaking point."
:: Age UK is calling on people to send a donation by calling 0800 169 8787 or texting HELLO to 70004 to donate £3 or visiting www.ageuk.org.uk/get-involved/loneliness.