Edinburgh International Book Festival has come under threat due to the impact of heavy rainfall on the city’s most historic garden.

A ‘negative’ environmental impact on the 200-year-old Charlotte Square Garden, as a result of increasing visitor numbers and poor weather, has been cited as the main concern surrounding the event’s future.

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Festival organisers said they are ‘very concerned’ about the gradually declining condition of the garden and admitted it has been ‘impossible’ to carry out vital reinstatement work since October, due to the privately-owned park being repeatedly waterlogged.

They fear attempting to re-turf the garden while it is still waterlogged will cause ‘long-term damage’ to the ground.

Organisers also claimed the growing difficulties in bringing the garden, which attracted a record 265,000 visitors in August, back up to scratch “cannot continue indefinitely”.

The festival, which expanded into George Street three years ago, has admitted “long-term investment” is needed to ensure that it remains in the garden, where it has been staged since it began in 1983.

It was initially held every second year, but has been annual since 1997.

The square, which was the last section of the first phase of the city’s New Town to be completed in 1820, is described by the Edinburgh World Heritage trust as “one of the finest architectural set-pieces in Europe”.

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A festival spokeswoman told The Scotsman: “We’re very concerned about the impact we have on this magnificent and historically important garden square in the heart of Georgian Edinburgh.

“As the festival grows, and attracts more visitors, the ground on which it resides is unfortunately being affected.

“Weather conditions in 2019 were particularly challenging.

“Between July and December, 258mm of rain fell upon Edinburgh compared to 91mm in 2018 and 52mm in 2017.

“Conditions have not improved since Christmas.

“As a consequence, reinstating the garden has proved impossible.

“Any attempt to re-turf it while it remains waterlogged would cause long-term damage to the soil structure.”

The festival has been in talks for years with the Charlotte Square Proprietors Association (CSPA) over the declining condition of the garden.

However, an agreement has not been reached on how the garden could have new infrastructure installed and a new management regime put in place.

The festival spokeswoman added: “While we reinstate the gardens each year following the festival, we are aware that this situation cannot continue indefinitely.”

A spokesman for the CSPA said: “It is unfortunate that the normally rapid reinstatement programme by the book festival has been severely delayed by the wet weather.

“Strenuous efforts are being made to ensure that a means of avoiding this problem in the future is found.”

However, Cliff Hague, chair of the Cockburn Association heritage body, said: “The negative impact that the book festival has on Charlotte Square Gardens is a snapshot of the wider challenges facing Edinburgh and other tourist cities that have become victims of their own success.”