People have been warned to watch out for scammers pretending they are police.

Hertfordshire Constabulary say fraudsters are calling victims via landline and claim to be a police officer asking for assistance with an investigation.

The scammers then ask the victims to withdraw a large amount of money and give it to a courier who would come to their home.

The force is urging people to be vigilant in the wake of the scam calls.

Inspector Victoria Richards said: “Luckily, many people recognise that these calls are fraudulent and refuse to hand over any money.

“However, there are some occasions where people fall prey to the highly persuasive nature of these scammers, and unfortunately lose thousands of pounds.”

“I want to take this opportunity to stress that police would NEVER ask you to withdraw money as part of an investigation and hand it to a courier.

“Please help us to raise awareness by sharing this with your friends and family, especially if they are vulnerable or elderly. If you do receive one of these fraudulent telephone calls, please make sure you report it to us as soon as possible.”

Hertfordshire Constabulary offers the following crime prevention advice:

• Be sceptical of callers, even those who claim to be officials.

• Don’t be afraid to put the phone down with a brief ‘No, thank you’.

• NEVER give personal information, such as your date of birth or bank details, to unexpected callers.

• Remember that the police or your bank would NEVER unexpectedly call you and ask you to withdraw cash or move your money to another account, as a result of fraud or any other reason.

• If callers suggest you call your local police or bank to check who they are, use another phone or ensure the line has been fully disconnected by phoning a friend or relative first, or by waiting at least five minutes, otherwise you may think you’ve phoned a number, but you’re simply talking to the fraudsters again. This is a common fraudsters’ tactic.

• If a caller asks you to type your bank PIN number into your telephone handset - do not do this, as fraudsters can use technology to identify the numbers.

• You can opt out of many cold calls by registering for free with the Telephone Preference Service on 0845 070 0707.