Prof Stefan Buczacki, the former chairman of Gardener’s Question Time, branded the advice “utterly bizarre”.
The 77-year-old author of more than 50 books on gardening and natural history said: “I find the warnings extraordinary. They just seem to have dreamt them up out of nowhere.
“Glass is a much better, more efficient material for greenhouses because it heats up much quicker than polycarbonate.
“That is why big commercial growers still use glasshouses.”
Similarly, Chris Collins, a former Blue Peter gardener, said: “I would prefer a glasshouse. They are more effective and polycarbonate is really expensive.
“If a strong wind sweeps through some glasshouses don’t look too stable, so I wouldn’t want to be under one on a windy day.
“But to stop using glass because they’re worried about safety and litigation is a bit much.”
But the Society’s recently published guide, 21st Century Allotments in New Developments, singles out “glass in greenhouses, cold frames and cloches” as unsafe design features.
It warns: ‘”Broken glass, especially when shattered and lurking in soil, causes innumerable injury to allotment gardeners, their visitors, domestic pets and wildlife.
“Safer alternatives are polytunnels and/or greenhouses and cold frames made with polycarbonate.”
It also highlights internal fencing between plots and bonfires as further potential hazards to be avoided for fear of accidents on allotments.
Advice likely to inform council rules around the country
Phil Gomersall, the society’s president, explained: “We want allotments to be as safe as possible.
“Glasshouses are a bit flimsy unless you pay a lot of money for them and a lot of people on allotments don’t.
“One of the big issues when you go on sites is broken glass. I am still finding bits of glass after 20 years on my allotment.
“You only have to be rooting around in the soil with bare hands and you can easily suffer cuts.”