Rising car use and cuts to public funding are being blamed for a loss of 134 million miles of coverage over the past decade alone.
Some cut-off communities have taken to starting their own services, with Wales and north-west England hardest hit.
The government has encouraged councils and bus companies to work together to halt the decline.
One lobbying group fears the scale of the miles lost are a sign buses are on course to be cut to the same extent railways were in the 1960s.
During that decade thousands of miles of track were scrapped and hundreds of stations closed following a report by British Railways Board chairman Dr Richard Beeching.
Chris Todd, of the Campaign for Better Transport, said: “We are not talking a loss of that level, but we are heading that way.
“We live in a society that is quite prepared to completely abandon certain groups of people and leave them with no options of getting around.”
Communities around the UK say the shrinking bus network is leaving people unable to reach basic services such as shops and GP surgeries.
Our comment: How much bigger might the decline in services be without the English National Concessionary Travel Scheme which was introduced nationally in 2008 ? Crises of viability of local bus services throughout England are likely to have arisen from one end of the country to the other.