Past victims of fraud are being targeted repeatedly by a new scam letter and email referencing the prior incident, warns Action Fraud.

The scammers are posing as the City of London Police's National Fraud Intelligence Bureau (NFIB) and claiming to be able to help get back the money they’ve lost.

It suggests that the criminals have now been caught and all you need to get a refund is to share your personal details.

But the emails and letters are bogus and scammers are trying to dupe vulnerable victims into sharing personal bank details that can be used to defraud them again.

[Read more: New Microsoft scam warning – all you need to know]

What it looks like

It's not the first time scammers have imitated the police. Here’s what the latest scam letter looks like:

Fraud Monsters scam letter example (Image: Action Fraud)

Source: Fraud Squads UK by City of London Police

The letter appears to be from the City of London Police and uses the branding as well as the City of London Police Commissioner's name.

But there are obvious signs it’s a scam.

Apart from the poor grammar the language is over the top and refers to the criminals as ‘fraud monsters’.

The City of London Police said in their Facebook post that these should be warning signs: “We don't tend to write to victims about "fraud monsters", so if you get a letter or email claiming to be from City of London PoliceAction Fraud or your local police force with spelling and grammar as bad as this one we've just come across, please be careful.”

The letter also asks you to share your personal details with a South African bank, which should obviously set off alarm bells.

City of London Police’s Detective Chief Inspector Andy Fyfe told the FT Adviser: "This fraudulent letter is clearly not something that the National Fraud Intelligence Bureau would send to the public. 

"It takes advantage of peoples’ trust in order to steal money from those who have already fallen victim.

"By using recognised organisations, including the National Fraud Intelligence Bureau’s branding and the City of London Police’s reputation, the fraudsters are attempting to appear credible. 

"If you are unsure about a letter you have received from the National Fraud Intelligence Bureau, please contact Action Fraud directly before giving away any of your personal details."

How to keep safe

Fraudsters are known to contact past victims pretending to be from law enforcement or government agencies who claim they can help you recover the stolen money.

If you've received a letter, email or phone call that doesn't look or sound right, think twice before handing over any of your details.

City of London Police and Action Fraud or any other police force would never ask for personal details or an admin fee to help recover previous losses.

If you suspect a letter or email you receive is bogus make sure you don’t follow any links or call any numbers supplied in the correspondence.

Instead, ignore it and contact Action Fraud to report it.

[More on scams and how to avoid them]