The need for urban growth has led to green belt land being nibbled away in Burnley, figures reveal.
The Campaign to Protect Rural England pressure group has called urban sprawl "a cause for concern" that risks ruining the countryside.
In 2017, about 10% of land in Burnley – 11 square kilometres – fell inside the green belt, according to recently released data from the Ministry of Housing, Communities and Local Government.
The scenic sites around large urban areas preserve rural land, and while they can be developed are subject to tight building controls.
The figures show that agriculture is most prevalent within Burnley's green belt, taking up 67% of that area.
In second place are forests, open land and bodies of water, which take up 17%.
Overall, 8% of land within Burnley's green belt boundary is now classed as developed, with homes, offices and rubbish dumps among the uses. This compares to 8% across England.
A further 460,000 homes have also been planned on green belt lands.
Rebecca Pullinger, from the Campaign to Protect Rural England, said previously developed brownfield land provides enough room for new houses.
She added: "There is space on brownfield land for more than 1 million new homes, but if its potential is to be fully realised, the Government, councils and house builders must all take a brownfield-first approach to development.
"We should also be investing in the green belt to improve its value as a vital public resource, enhancing nature by planting trees and restoring wetlands, and improving access and accessibility so more people than ever can enjoy its benefits."
A spokesman for the Ministry of Housing, Communities and Local Government said: "We are clear that building the homes our country needs does not mean tearing up our countryside. In fact the green belt is around 30,000 hectares larger than in 1997.
"Last year only 0.02% of the green belt was developed for residential use and often this development is around road and rail infrastructure in place long before green belt designation."