Busy lives and hectic work schedules are the main reasons people are eating more alone, according to a survey commissioned by The Big Lunch.
Robert Palmer, chef and co-owner of the Dorset Arms, Lewes, East Sussex, said solo diners are a frequent occurrence at his pub.
He said: "It always seems a bit odd when we get solo diners in and it is always questioned by the kitchen staff, thinking that the floor staff have messed up."
Solo diners tend to come in earlier in the week and order, on average, two courses, he said, adding that they were neither disproportionately male nor female.
Pubs were ideally positioned to cater to solo diners, added co-owner Paul Bennett.
"Being less formal, people don't feel scrutinised or self-conscious for dining alone."
Despite the number of Brits choosing to dine alone, people are more likely to feel happier with their lives when they frequently ate with company, The Big Lunch's report said.
Peter Stewart, of The Big Lunch, said: "The amount of solitary meals eaten each week is shocking, especially as the study shows that sharing food helps feelings of closeness and friendship."
One fifth of respondents said they had not eaten an evening meal out in a pub or restaurants with a good friend or family member in over six months.
Robin Dunbar, professor of psychology at Oxford University, said: "This study shows that, in the UK, we are becoming less socially engaged, with almost 50% of meals eaten alone each week.
"In these increasingly fraught times, when community cohesion is ever more important, making time for and joining in communal meals is perhaps the single most important thing we can do."
The Publican's Morning Advertiser reported last week that British customers are becoming more inclined to 'menu hack' when dining out, with 28% claiming they would order completely off-menu in a pub or restaurant.