The elderly have been warned to be on their guard against bogus retail and investment schemes targeting the older generations. .

The Insolvency Service has shut down 78 rogue companies that raked in over £28 million were shut down in England and Wales in the last three years. Information it obtained showed the oldest victim was 92.

Forty-nine of the companies sold plots of land for "building" that either did not exist or were on protected green belt land. Four sold wine stocks that did not yield any profits, and 19 sold other forms of investment.

Six sold retail products that were either unsuitable or at highly inflated prices, including burglar alarms, mobility scooters, "heritage" coins and stair-lifts.

Between them, the companies, which represent around one in 10 of more than 800 companies wound up by the Insolvency Service in the three years between April 2009 and March 2012, scammed close to 2,000 investors.

The Insolvency Service is being supported by three charities - Age UK, Alzheimer's Society and Action on Elder Abuse - to warn the public about these scams, on the day that campaign actions to highlight World Elder Abuse Awareness Day are taking place.

Business minister Norman Lamb said: "These scams are especially bad as they target some of the most vulnerable members in our society. Older people have grown up trusting other people. To take advantage of this trust and then exploit it is both manipulative and deceitful.

Robert Burns, head of investigation and enforcement for the Insolvency Service, said: "We have observed a number of companies targeting older people in recent months.

"These scams are particularly unpleasant because they target the most susceptible members of society, older people who may be unsure how to seek advice or afraid to say 'no'.

"They can destroy lives at a time when those targeted should be taking a break from worry and enjoying life after working hard.

"The worst aspect is the callousness with which the fraudsters go about their business; ignoring the obvious fact that that because of their age, most victims will never be able to make good their loss.

"If you are cold-called, don't be afraid to say 'no, thank you'. If in doubt, you should take time to research the company and get some independent advice.

"Today is World Elder Abuse Awareness Day and we would urge all friends, carers and family members to be vigilant and look out for the older members of their family to ensure that they are not scammed by rogue businessmen."

Alzheimer's Society is also campaigning against the financial abuse of people with dementia.

Chief executive Jeremy Hughes said: "There are currently 800,000 people living with dementia in the UK. Many are older people and easy targets for con artists.

"It is disgusting that these scams specifically target the most vulnerable in our society. Con artists are dealing another blow to people who may already be struggling financially due to the huge cost of care.