A poll for the walking charity the Ramblers suggests 25% of adults walk for no more than one hour each week.
The YouGov survey, which polled 2,000 adults across Britain about walking habits, found another 43% reported walking for less than two hours a week.
Government guidelines suggest people should do 150 minutes of “moderate” physical activity each week.
The survey asked people about the total amount of walking they did, including trips to school, work or the shops.
The Ramblers, which is promoting a “Get Walking Week” from 4-11 May, said there was already research showing that two thirds of adults in the UK do too little exercise.
It said the survey backed that up.
The West Midlands was revealed as the worst region for weekly walking, with more than a third of adults (34%) walking for no more than an hour a week.
The East Midlands came out top, with 59% of people doing enough to satisfy recommended physical activity guidelines.
Despite the low levels of walking reported, nearly all of those surveyed – 93% – agreed walking was a good form of exercise.
The Ramblers charity, which promotes walking for health and pleasure, is seeking to get people to go on walks of five miles or less and has free walks led by guides.
Benedict Southworth, chief executive of the Ramblers, said: “We want people all over Britain to join the walking revolution and take their first steps towards a healthier and happier lifestyle.
“Walking is one of the most accessible and achievable ways to truly conquer this inactivity pandemic in Britain, and we need to get started now.”
Public health minister Anna Soubry, said walking was “one of the best ways to keep healthy”, and that she supported the initiative.
The British Heart Foundation (BHF) advises that moderate intensity aerobic activity is the most effective type of activity for maintaining a healthy heart.
Aerobic activity is a repetitive rhythmic exercise involving large muscle groups such as legs, shoulders and arms.
Moderate intensity activities should make a person feel warmer, breathe harder and make their heart beat faster than usual. But, they should still be able to have a conversation.
The BHF also advises 150 minutes of moderate intensity aerobic activity each week.