University of Exeter researchers used Google Earth and Google Street View to estimate that verges account for 2,579 km2 (almost 1,000 square miles) of land.
About 27% of these verges are frequently mown, 41% is wilder grassland, 19% is woodland and the rest is scrub.
There are "significant opportunities" to improve verges by reducing mowing and planting trees, the researchers say.
"Our key message is that there's a lot of road verge in Great Britain and we could manage it much better for nature," said lead author Ben Phillips, of the Environment and Sustainability Institute on Exeter's Penryn Campus in Cornwall.
"About a quarter of our road verges are mown very regularly to make them look like garden lawns – this is bad for wildlife."
Read more at: University of Exeter
Road verge (Photo Credit: Ben Phillips)