Britain could enjoy 400bn more flowers if road verges were cut later and less often according to guidelines drawn up by wildlife charities, highways authorities and contractors.

The national guidance for managing roadside verges for wildflowers calls for just two cuts a year – instead of four or more – and only after flowers have set seed, to restore floral diversity and save councils money. It would also provide grassland habitat the size of London, Birmingham, Manchester, Cardiff and Edinburgh combined.

The recommendations have been produced by the wildlife charity Plantlife, backed by national highways agencies, the industry bodies Skanska and Kier, as well as Natural England and other environmental groups.

With 97% of wildflower meadows in Britain having been destroyed in less than a century, roadside grassland has become a crucial wildlife habitat for more than 700 species of wildflowers – nearly 45% of our total flora – including 29 of 52 species of wild orchid such as the rare lizard orchid.

Roadside verges are increasingly important “wildlife corridors”, assisting the movement of plants, flowers and invertebrates across an increasingly fragmented countryside. But there has been a 20% decrease in floral diversity on road verges since 1990, in part because of overzealous cutting.

Trevor Dines, a botanical specialist at Plantlife, said: “Publishing these new guidelines endorsed by so many influential players is an exciting step forward. Widespread adoption of this best practice management by councils and their contractors could transform our road verge network.

“Grassy verges cover an area equivalent to all our remaining lowland species-rich grassland so this new approach can literally double the opportunities for wildflowers and wildlife.”

Matt Tompsett, the senior environment and sustainability manager at Kier, said: “For too long our roadside verges have been neglected and under-utilised, with their potential as wildlife havens and corridors unrealised. These new guidelines demonstrate just how easily this can be changed with some simple tweaks to management regimes helping to achieve biodiversity net gain and a save a little money in the process.”

Road verges can be designed and managed to support an array of wildlife, say conservationists. Photograph: Emma Adams/Alamy

The guidance recommends different numbers of cuts depending on the type of grassland but with several key principles – no cutting before the end of July, and the removal of all grass cuttings to lower soil fertility and allow a more diverse range of wildflowers to flourish.

The guidelines concede that some residents and road users view wildflower-rich verges as “untidy and neglected” but says managers can cut narrow strips around the wilder verges to frame them – “a simple but effective way to give the perception of tidiness and help offset potential negative feedback”.

Clare Warburton, the principal green infrastructure adviser for Natural England, welcomed the “cost-effective, practical solutions” in the new guidance. “Road verges can be designed and managed to support an array of wildlife, as well as helping us tune into nature on our daily walk, cycle or drive,” she said.

“A great multitasker, nature on the road verge does a number of jobs like cleaning the air, storing carbon, pollinating crops and providing sustainable drainage.”

Phil Sterling, a programme manager at Butterfly Conservation, said: “The new guidance provides practical, realistic and affordable examples of how to turn road verges into wildlife corridors.

“We can and must change the way we create and manage road verges, to encourage wildflowers, butterflies, moths and other insects. The guidance also shows it can cost us less to do exactly that.”

Red clover and lady’s bedstraw, two of the roadside wildflowers that support the highest number of invertebrates, are among the plants experiencing the most rapid decline.

According to Plantlife, wildlife-friendly management of verges has saved councils money in recent years, with Dorset council estimating it reduced the cost of verge management by more than £100,000 since 2004.