Conmen used their charms to trick elderly victims into handing over cash in five incidents in the space of 48 hours.
The five incidents took place last weekend where elderly people were tricked into giving away their bank details, and included one case where the victim handed over £3,000.
Police in the county are reminding people that they should never give their bank details to anyone who has phoned them, no matter who they claim to be.
In a number of instances offenders have claimed to be police officers who are investigating a fraud and ask for the victims’ card and bank details so they can check with the bank.
They also tell the victims they will send a courier to pick up their bank card and any cash they may have recently withdrawn, in case it is counterfeit.
Another ploy used by the criminals is to persuade the victims to make an online transfer of cash.
Bryan Pye from the fraud and financial investigation team of the East Midlands Special Operations Unit said: “We want people to be aware of these cons so they don’t fall for the charms of the people at the other end of the phone line when they call.
“Many of the victims of this type of crime are elderly and it can be very distressing for them.
“In no circumstances will police officers call you and ask for your bank details.
“And in no circumstances do we ever use couriers to collect evidence from victims of crime.
“Likewise, your bank will not phone and ask you for your bank details – they already have them.
“Our advice is to hang up the phone if someone starts asking you for your card or bank details and call 101 to report it to us.
“Don’t worry about offending the other person at the end of the phone - they won’t worry about taking your money.”
If people are concerned they are a genuine caller and their bank account has been accessed they are encouraged to visit their bank in person.
If there have been illegal transactions on an account then the bank will have put a stop on the card so no more money can be withdrawn, while an investigation takes place.
Mr Pye added: “In some cases the con men told the victim to hang up and call them back, so they can be reassured they are genuine.
“This is part of the con.
“The offender will keep the phone line open at their end so when the victim makes the phone call, they go straight back through to them.
“For this reason we are telling people who are worried about any calls they may have received to visit their bank to check their account or to call from another phone line.”