Rainforest plants housed in Kew Gardens could be scorched as temperatures soar close to 40C, one of its executives has said.

Richard Barley, director of gardens, said the Palm House was kept cooler than the outside temperature but “leaf scorch” was still a risk.

“A building like the Palm House doesn’t have structural shading or anything of that sort, so scorching is a possibility,” he said.

“If there’s no cloud cover and if the air temperature is high and there’s sunshine in mid-summer conditions, we can get leaf scorch, particularly of plants that have their foliage up close to the glass.

“Usually, the plants will withstand reasonably high temperatures, although if they got to be extreme, we’d be in uncharted territory.”

Visitors appeared to be put off by the temperatures as they soared into the high 30s, with Mr Barley suggesting most had “sensibly stayed” in the “comparative cool” of their homes.

However, the Palm House was cooler than the outside conditions thanks to its humidity, which is maintained at around 75%.

“The staff will hose down the plants in the morning so that it’s as if there’s been a heavy rain shower come through, as there often would in the tropical jungles,” Mr Barley explained.

“A lot of that water will also fall to the floor surfaces and it will evaporate off those surfaces and that helps to cool the building.

“It assaults your senses with the humidity and the smell of the plants – you just feel you’re somewhere in the world that isn’t west London.”