This was the view after a ton of wood from a windmill sail crashed through the roof of a museum, spraying debris onto parked cars.

The sail smashed through the roof of the Grade II-listed Windmill Museum on Wimbledon Common at about 6.45pm yesterday.

Keeper John Shipton, who lives next to the museum, heard an "almighty crash" and discovered the damage.

He immediately called members of the Wimbledon and Putney Commons Conservators, who worked together to make the area safe.

Fortunately, no-one was injured. The museum had been closed because neighbouring Parkside was blocked to cars during the Prudential RideLondon cycle race.

Two cars belonging to Mr Shipton and his guest were scratched by pieces of terracotta from the chimney stack which flew 10 metres from the roof.

Simon Lee, chief executive of Wimbledon and Putney Commons Conservators, which owns the windmill, said: "I had been sitting in my garden at midday watching it because I love to see the cap turn.

"Then, when I came back later I saw that it was seriously damaged. It's very sad."

Most damage was caused to the chimney and roof. Fortunately display cabinets containing historic documents were not smashed.

Fifty thousand pounds had already been set aside in April to restore the water-damaged wooden structure on the first floor.

The Conservators are now considering launching a fundraising appeal to restore the windmill sail, which Mr Lee said was likely to cost "many thousands of pounds".

Architect Norman Plastow, 85, who restored the windmill in 1975, rushed from his house to the Common as soon as he heard the news.

He said: "We are very fortunate because none of the exhibits in the museum were damaged in spite of being covered in pieces of roofing."

He said he thought the damage was caused by rot from water getting into the timber.

The windmill is inspected every year by a millwright, who was due to complete this year's inspection this summer.

The museum will be closed while repairs are carried out. The Windmill Cafe remains open, but a millwright due to visit the windmill today will make another safety assessment.

The windmill was built in 1817 by carpenter Charles March as a corn mill. It was converted into cottages in the 1860s, when Earl Spencer, the Lord of the Manor of Wimbledon, bought a section of the Common.

In 1975 it was restored by Mr Plastow after a public appeal was launched to raise £20,000.

Sail down: The Windmill before and after the incident

It has been a museum since 1976, displaying different types of windmill and an extensive collection of woodworking tools.

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