Thieves have stolen a bronze plaque remembering the heroes who fought in both World Wars and died at Cane Hill asylum.

The monument, in the garden of remembrance at Croydon Cemetery, Mitcham Road, is a tribute to the estimated 3,000 patients who died at the mental health hospital in Coulsdon, between 1884 and 1950 including 26 war veterans.

The bodies of inmates unable to afford a full burial at the Cane Hill site were cremated and re-interred at the cemetery in 1981.

Adrian Falks, who led the campaign to have the Cane Hill residents recognised, said: "That plaque took 29 years to erect.

"The person who stole it hasn’t simply insulted the memory of the poor, he has insulted the monarch, and the memories of people who fought and died for this country.

"It is an unspeakable desecration."

Through work from Mr Falks in a campaign supported by the Croydon Guardian, men interred at Mitcham Road were recognised as veterans by the Commonwealth War Graves Commission in August.

Peter Taylor, who was also involved in securing recognition for the soldiers, visited the cemetery on October 2 and was appalled to see it gone.

He said: "Now soldiers' names are on the Debt of Honour on-line register, this is a war grave, and theft is tantamount to an act of desecration."

Metropolitan police are investigating after 66 bronze plaques, including the Cane Hill memorial, were stolen on September 27.

The plaque was installed in February 2009, with companies Phoenix Foundries and JB Shakespeare providing the granite base and Croydon Council providing the ground work.

Since then, Mr Falks has laid a wreath at the site on Remembrance Day, now less than a month away, in honour of the soldiers.

A spokesman for the council confirmed they were concerned about the recent plaque thefts, with a further 150 plaques taken in June, and were investigating replacing the Cane Hill memorial.

He said: “We are in the process of looking at options for replacement and the possibilities for any additional security.

“In the meantime we are obviously keen to hear from anyone who has any information regarding these exceptionally upsetting and callous thefts.”