A vision of a blazing bridge has won a tongue-in-cheek competition seeking "alternative but equally ridiculous" design proposals that could replace Thomas Heatherwick's much maligned Garden Bridge for London.

Over 50 alternative proposals were submitted to the open-call competition named A Folly for London, which sought to parody designer Thomas Heatherwick's controversial River Thames crossing – currently under judicial review.

Led by political artist Will Jennings, the contest called for proposals that use environmentally damaging materials for a site on the South Bank. Applicants were also asked to obscure as many of the views as they could, to a budget of £60 million.

This figure is in line with the public funding element pledged by London's mayor Boris Johnson towards the construction of the £175 million Garden Bridge, which has been touted by Westminster council as the "most expensive footbridge in the world".

"In celebration of great British satire, this competition is an opportunity to propose an alternative but equally ridiculous project for the public space being lost to the proposed Garden Bridge on London's South Bank," reads the text on the competition website.

The winning entry, Green Fire Of London by Ben Weir, imagines an eternal bonfire on the River Thames.

Designed to be fuelled by trees felled from London's parks, the scheme is described as "an eternal flame dedicated to 21st-century planning departments and developers".

The newly razed parks would be freed up as invaluable land for private development, while the burning fire would create a smokescreen to obscure views of the Thames.

"The project is fuelled in a completely sustainable green manner however, as timber is a renewable energy source," said Weir.

Weir has been awarded a framed image by Martin Rowson, the political cartoonist for the Guardian, who was one of the three judges of A Folly For London, alongside Green Party leader Natalie Bennett, and architecture critic and Dezeen columnist Owen Hatherley.

Runners up in the competition are a pair of projects named Bulb Anthropophagic by Architecture Anonymous and Floating Tidal Exploded Bus Maze by Chris Doray Studio, while honourable mentions were given to several others.

Hatherley praised the entrants for the "scorn, humour and imagination" present in their designs. "The Garden Bridge is the sort of whimsical, thoughtless project you'd expect a slightly dim architecture student to reject," he said.

"The three winners all responded with projects that combined satirical silliness with warnings for the future London is making for itself – destroying real public space and replacing it with tourist tat, decimating its social infrastructure for photo opportunities and property development," added Hatherley. "May they shame the Garden Bridge out of existence."

Arseholes by Roly Tee and Scrotopolis – a toll bridge modelled on a "pallid pink erection" – by Huren Marsh were acknowledged by the judges for its priapic humour.

Jesus Square & Bridge by Andrius Daujotas and Tautvilė Džiugytė – an invisible bridge allowing commuters to walk on water – and Devil's Bridges by Valentina Kholoshenko and Valeriia Potashko were commended for their efforts at absurd transport infrastructure.

For feigning environmentally friendly design, the Greenwash award was presented to three joint winners: Huge Cake by Shimokawa Shohei, The Fairy Mushroom by Anna Pro & Kira Olkhovsky and the rainbow-hued Bifrost Bridge by Charlie Plumley.

"They had fully grasped the need to highlight the absurdity of the Garden Bridge project, which is cutting down trees and destroying a public green area to create a privatised artificial, view-blocking structure, funded with transport money when cycles won't be allowed and pedestrians barred from it overnight," said Bennett.

The proposals will be exhibited at St John's Church in Waterloo from 24 September until 4 October 2015.

The 366-metre-long Garden Bridge won planning permission from the London boroughs of Westminster and Lambeth at the end of 2014. But the project cannot currently move forward, as Lambeth resident Michael Ball – the former director of charity and community planning organisation Waterloo Community Development Group – has lodged a legal challenge, claiming that planning permission was obtained unlawfully, ignoring issues regarding funding.

Helsinki's contentious Guggenheim museum competition attracted similar scepticism. Earlier this year, architect and writer Michael Sorkin teamed up with Finnish architects and artists to launch a rival competition called The Next Helsinki.