The seven things Department for Work and Pensions look out for in bank accounts and on social media to spot benefit fraud have been revealed.
A crackdown operation is being launched by investigators after £8.4bn was overpaid in the last financial year.
DWP bosses say fraud and error in the UK benefits system reached record levels during the pandemic with estimates that 3.9% of benefits spending was overpaid during 2020/21.
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Around 23m people are currently on DWP pay-outs, including 12.4m who claim state pension and almost 6m of whom claim Universal Credit.
There are also 2.9m people claiming housing benefit, 2.7m on Personal Independence Payment (PIP) and 1.8m people claiming Employment and Support Allowance (ESA).
Neil Couling, Universal Credit director-general, stated that the DWP's fraud and error probe could see thousands of claimants approached over the coming months.
Investigators can turn up at your home or workplace at any time in plain clothes if they suspect foul play, The Mirror reports.
They also use a range of powers to gather evidence such as surveillance, document tracing, interviews, checking your bank accounts and monitoring your social media.
The DWP said: "In simple terms an overpayment is benefit that the claimant has received but is not entitled to.
"Overpayments of benefit can occur in a number of ways. In the main they are due to claimant, system or official error."
The DWP has outlined seven types of overpayments it looks for:
In each of those cases, the DWP can make efforts to get the money back under Social Security legislation.
You may be taken to court where a fine of up to £5,000 can be imposed. A person's benefits can be cut for up to three years if they are convicted of benefit fraud.
A DWP spokesman said: "We take any abuse of taxpayers' money very seriously and those who claim benefits they are not entitled to will face criminal prosecution.
"We also have robust plans in place to recover fraudulent claims and drive fraud and error down to the lowest feasible level."
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