It survived the Blitz, several lightning strikes and threats of demolition but now Shirley Windmill is being gradually destroyed by a new enemy – parrots.

Rose-ringed parakeets have been sharpening their beaks on the 150-year-old windmill’s sails, causing thousands of pounds worth of damage.

Volunteers who work at the mill during open days say that some damage has been inflicted on the timber sails, which cost about £50,000 for a set of four.

John Jackson, chairman of the friends of Shirley Windmill, said: “Croydon Council are monitoring the damage carefully. It is not too bad at the moment but if it becomes a health and safety issue we may have to close the mill to the public.

“Replacing the sails would be hugely expensive, even just replacing the individual timber struts would be a big job.”

In July, the Croydon Guardian reported that the parakeets have caused about £10,000 worth of damage to the spire of St John’s church in Shirley by pecking at the shingle.

The birds, which come from Africa and Asia, are not native to Britain. It is thought that they started breeding in London in the 1950s.

One theory is that a whole flock of the birds escaped from Shepperton Studios in Surrey from the set of The African Queen, starring Humphrey Bogart and Katherine Hepburn.

Mr Jackson said: “They are a nuisance but I have to admit they are pretty impressive.

“I saw two of them dive bomb an pigeon the other day, they saw him off in no time at all.”

Mr Jackson said that they have no idea how to get rid of the birds, so will just have to keep monitoring the damage to the sails.

Apart from the parakeets, the mill suffered two air strikes during the Second World War.

The mill had to be rebuilt in 1854 to replace the previous mill that burned down in a fire. It has also been struck numerous times by lightning.

The windmill, at the top of Postmill Close off Upper Shirley Road, is open to visitors over the summer every year.

The last open day for this year will take place on Sunday.