Potential victims are being warned to be on guard after phone fraudsters after 21 people were contacted in the space of 24 hours.

Residents in Steeple Bumpstead were among householders in Essex who were called by scammers pretending to be police officers.

The latest spate of calls took place between Monday evening and Tuesday afternoon.

Most of the victims realised the calls were fraudulent, but one man in Dedham, near Colchester, was tricked into handing over credit and bank cards.

Criminals withdrew £2,500 from a local ATM before the cards were stopped.

In all cases the caller claimed to be either a detective from either the Metropolitan Police or Essex Police.

DCI Paul Maleary, who is leading the investigation into the frauds, said: "These criminals are having a significant impact on some of the most vulnerable members of our society and sadly no individual is immune from this type of fraud.

"These thieves keep varying their stories and trying different tricks to encourage people to hand over bank details or large sums of cash.

"All their claims are absolute rubbish because the police and banks would never ask for details over the phone then send a courier to collect cards or cash.”

Almost 700 thefts and attempted thefts have been reported in Essex since the scam first came to light last January.

More than 100 people in the county have been tricked out of money, with more than £355,000 being stolen in total.

Six people have been arrested in connection with the investigation.