The study suggests more than 2.3 million dogs are routinely left in solitude for five or more hours - despite vets advising four hours as the absolute limit.
And the research shows 465,000 dogs are never even taken for a walk and, as a result, are at risk of mental health problems.
Vets say a daily walk and meetings with other dogs are essential for the well-being of hounds who are naturally sociable animals.
Experts say loneliness can lead dogs to developing destructive behaviour, as well as anxiety and frustration.
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But the latest PDSA Animal Well-Being Report shows 28 per cent of UK dog owners surveyed believe it is acceptable to regularly leave a dog alone in the house for anything between six and 10 hours at a time.
Experts say too many dog owners are allowing their hectic lives to get in the way of providing their pets with their basic needs.
Now vets are urging owners not to neglect their pets as they settle back into their working routine after the Christmas break.
PDSA vet Vicki Larkham-Jones, said: “These are very worrying findings and the fact that people think it’s acceptable to leave their dog alone for so long is especially concerning.
“Lonely, frustrated dogs may be more likely to demonstrate problem or unwanted behaviour and over 50 per cent of UK veterinary professionals report having seen an increase in dog euthanasia due to behavioural issues in the past two years.”
She added: “PDSA is urging pet owners to re-assess life from their pet’s perspective to ensure that they are giving their animals the right level of care and attention they need to live healthy, happy lives.
“I’d encourage people thinking about getting a pet to pause first and find out about all aspects of pet ownership in order to provide for that animal’s lifetime needs.”
More than 31,500 pet owners were surveyed as part of the research.