GOV.UK
Discovery Decisions: Discovery - Extending an enquiry under S19
It is an accepted principle of long standing that evidence that something is incorrect for one year allows you to infer that earlier years may also have been wrong. So where your enquiry into the entitlement for a year under S19 leads you to believe that the entitlement for that year was incorrect, you should always consider whether the same errors may have occurred in earlier years. But you will need to satisfy yourself that any inferences you are drawing about the earlier years are reasonable in the circumstances of your particular enquiry.
During your enquiry you will have obtained evidence about the claimant’s circumstances and / or income, including how long those circumstances have prevailed. For example, you may have established that the claimant was a member of a couple during the year, and should not have made a claim as an individual. It may be reasonable, depending on the evidence you have, to infer that the couple was in existence during earlier years as well. Or you may consider that the couple did not form until the year you are enquiring into. In the first set of circumstances, you would be able to make a discovery decision as long as this amounted to fraud or neglect, but in the second you would not.