When a crack first appeared in one of the 785 windows of the Great Glasshouse of the National Botanic Gardens in Carmarthenshire almost three years ago, the garden’s publicist David Hardy knew that replacing it would be a “tricky operation”.

He said: “The pane measures roughly 4m x 1.5m (13ft 6in x 5ft) and weighs about half a tonne.

“The contractors, from Metallbau Fruhand, Germany, were probably working 40ft up for much of the operation.

“About 100 of the 785 windows in the roof open to regulate the humidity but two or three have been permanently stuck open.

[READ MORE]