Story highlights Proposal to build mushroom garden in disused tunnel wins "High Line for London" competition

Idea suggests use of tunnel under Oxford Street and would double as a pedestrian walkway

Competition inspired by New York's High Line with co-creators of the elevated park on the judging panel

London's abandoned rail and tube lines have been put to many novel uses down the years functioning as bomb shelters, impromptu party venues and film sets for Hollywood movies.

But a new idea to create a mushroom garden in a tunnel beneath Oxford Street is perhaps one of the more unconventional attempts to breathe new life into the UK capital's forgotten subterranean murk.

"Pop Down" imagines a section of the defunct "Mail Rail" tunnel -- a narrow gauge railway used for transporting mail around London which closed in 2003 -- being repurposed as a mushroom farm and pedestrian walkway lit at street level by glass-fiber, mushroom-shaped sculptures.

Its creators, London-based Fletcher Priest Architects , say underground tunnels provide the ideal environment for an urban mushroom farm and could supply pop-up "Funghi" cafes at the tunnel's entrance and exit.

The idea was recently awarded the top prize in the " High Line for London " competition run by the UK's Landscape Institute in partnership with the Mayor of London and the Garden Museum.

The competition, which attracted 170 submissions, was inspired by New York's High Line -- a derelict section of elevated railroad which has been transformed into a park -- with co-founders Joshua David and Robert Hammond joining the judging panel.

"The response to this competition shows how many ideas are just waiting to happen, on, over or under the streets of London," Hammond said in a statement.

Runner-up in the competition was " The Lido Line " by [Y/N] Studio which proposes turning a section of the Regent's Canal running from Little Venice to Limehouse into a public swimming area.

Other entries were also highly commended including an idea for a floating park/farm/wetland near Canary Wharf called "Barge Walk" and "Bridge-It" which envisions building parks over, under and besides existing railway lines.

"During this Olympic summer it was clear that London's public spaces are coming alive as never before. There is now a popular appetite for making our outdoors more useable and more wonderful," Penelope Curtis, director of Tate Britain said in a statement.