Almost three-quarters of older people in the UK are lonely and more than half of those have never spoken to anyone about how they feel, according to a survey carried out for the Jo Cox commision on loneliness.

The poll by Gransnet, the over-50s social networking site, also found that about seven in 10 (71%) respondents – average age 63 – said their close friends and family would be surprised or astonished to hear that they felt lonely.

Gransnet is one of nine organisations – including Age UK, the Alzheimer’s Society and the Silver Line helpline for older people – working to address the issue of loneliness in older people, which is the current focus of the commission, set up by Cox before her murder last June.

They are urging individuals and businesses to look for signs of loneliness and refer people to organisations that can help. But they also want people to take time to speak to neighbours, family, old friends or those they encounter randomly.

The chairs of the cross-party commission, the Labour MP Rachel Reeves and Conservative MP Seema Kennedy, said there was a stigma around loneliness that must be tackled.

“We all need to act and encourage older people to freely talk about their loneliness,” they said. “Everyone can play a part in ending loneliness among older people in their communities by simply starting a conversation with those around you.

“How we care and act for those around us could mean the difference between an older person just coping, to them loving and enjoying later life.”

Almost half (49%) of the 73% who described themselves as lonely in the online poll said they had been so for years, 11% said they had always felt lonely and 56% said they had never spoken about their loneliness to anyone.

Laura Alcock-Ferguson, the executive director of the Campaign to End Loneliness – another organisation working with the commission – said the percentage of lonely older people had stayed the same for five decades, but an ageing population meant the number was increasing in absolute terms.

“Loneliness is a serious public health issue and dealing with it will take the strain off the NHS and social care services,” she said.

Common trigger events said to have contributed to feelings of loneliness were bereavement, retirement and children leaving home. Being shy, living alone or far from family and low income were other commonly cited contributory factors.

The rise of social networking to the detriment of face-to-face interaction has been blamed for contributing to an “epidemic” of loneliness, but the survey of just over 1,000 people found it could also offer solace.

Almost three in five respondents (59%) said social media helped people feel less lonely and about eight in 10 (82%) said talking about loneliness was much easier when anonymous and online.

While the results indicate the potential benefits of online interaction, the older people are the less likely they are to have access to the internet, particularly women.

The commission is encouraging supporters and followers to post #happytochat on social media to create discussion around loneliness and for people to wear badges with the same slogan. Ultimately, they hope some customer-facing organisations will encourage their staff to wear the badges.

Respondents highlighted greater public awareness – a key goal of the commission – as the best way to combat loneliness.

Caroline Abrahams, charity director at Age UK, said: “There are reasons to believe that we can all do something to change things for the better: a simple thing like saying hello and having a chat can brighten up an older person’s day and do more good than most of us would ever guess.”

In coming months the commission will focus on loneliness in other groups, including men, people with disabilities, carers, refugees, children and parents.