Elderly people are increasingly being marked out as targets of financial abuse as figures showed that the number of theft and fraud cases rose sharply in a year. An estimated £18m ($25.6m) in cash and items was stolen from the elderly, according to UK-based charity Action on Elder Abuse (AEA).

A national helpline operated by AEA received 7,529 calls – up from 3,500 previously – from people who believed they were being financially exploited in 2015, an investigation by the Times has revealed. In the 12 months to March last year, adult social services recorded 21,935 allegations of theft and fraud against the elderly, of which 4,168 were made against carers.

Over 500,000 elderly people are victims of abuse each year in the UK. The most common offences include financial, physical and psychological abuse as well as neglect and experts are now advising families of elderly people to install hidden cameras their homes as a protective measure.

AEA chief executive Gary FitzGerald told the newspaper: "Theft from older people is on the increase and worryingly the thieves are often people they should be able to trust, care workers, family and so-called friends.

"When money or valuables go missing it can be too easy to assume that the older person is at fault and has made a mistake, but we would encourage people to be far more suspicious and to investigate further," he added.

"Hidden cameras are a proven way of checking out what is happening and gathering evidence and we would recommend people give serious consideration to this option. It is hard for a thief to blame the poor memory of the victim when caught red-handed on camera."

AEA's website notes that perpetrators of abuse are often known to the elderly victim and, in many cases, take advantage of a special relationship. In February, carer Melanie Harris, 44, was jailed for stealing £75,000 from 65-year-old Ted Carter, who had cerebral palsy.

Harris used the money to fund "a lavish lifestyle" which included luxury shopping trips and expensive haircuts. Last month four men and four women were jailed for over 11 years by Chester Crown Court after they were convicted of preying on the vulnerable and elderly for a range of offences, including theft, fraud and harassment.

Installing hidden cameras in a private home can help police build evidence and bring perpetrators of abuse against the elderly to justice. The president of the association of directors of adult social services, Ray James said: "Theft is always reported to the police but whether or not they prosecute comes down to the availability of evidence. The combination of vulnerable elderly people who have informal arrangements with carers to get them cash and who know their PIN makes it hard to get evidence."