A Charles Rennie Mackintosh masterpiece is at risk because it does not have a sprinker system to prevent fires, it has been claimed.

The concerns have emerged as donations worth £1m have been received after an appeal to save the Hill House in Helensburgh.

But there are now fears that the Charles Rennie Mackintosh-designed structure could suffer the same fate as the Glasgow School of Art's Mackintosh building, which was destroyed in the Glasgow Arts School blazed two weeks ago.

A safety specialist has urged that conservationists consider installing a sprinkler system at the property in Helensburgh as a matter or urgency during its £4.5 million renovation.

Work in renovating The Hill House, which was constructed between 1902 and 1904 and features many wooden wall panels, is due to begin next Thursday with a giant mesh box being constructed around the house.

It is expected to remain in place for at least five years, protecting the property from the worst of the weather.

Keith MacGillivray, chief executive of the British Automatic Fire Sprinkler Association, said that refurbishment work represented a "high risk" of fire damage. "It is our view that every heritage building is worth protecting," he said.

The property, the National Trust for Scotland (NTS) described as "Charles Rennie Mackintosh's architectural masterpiece" has been threatened by the effects of water penetration.

Mr MacGillivray told The Times: said the works present an "ideal time" to consider installing a fire suppression system.

"This would safeguard Hill House for the future and can be easily fitted," he said. "It just makes sense. Refurbishment is the riskiest time for a fire to occur."

Fritha Costain, the business manager at the National Trust of Scotland, said that a sprinkler system would run the risk of damaging delicate parts of the property's extensive furniture collection.

The Herald:

"The way we would deal with a fire is much more proactive than reactive," she said. "There are no naked flames or flammable materials permitted on site, and we have a detailed emergency plan in place with the local fire service. The Glasgow School of Art is a very different state of use to us."

The NTS appealed in February for £1.5m in donations towards the £4.5m total cost of the renovation project.

It said the appeal for funds to secure the building was one of the most ambitious in its history.

Once the mesh box is constructed, the site will open to the public.

Raised walkways will enable visitors to see every level of the house during the renovation work.