Martin Lewis' website claims that UK households can slash thousands from an important bill. A tip shared by the consumer champion's site saw one family get almost £20,000 refunded - and they were oblivious they'd been missing out on a 'little-known' discount before bagging the cash.

Paul, a reader of the MoneySavingExpert (MSE) newsletter, discovered he was entitled to a council tax reduction. After reading MSE's guidance, he'd learned about the discounts available for those with severe mental impairment (SMI) and how it applies to council tax bills.

The council tax discount for those designated as 'severely mentally impaired' (SMI) typically means at least a 25% cut in the affected household's council tax bill. The criteria for this classification include having a significant impairment in intellectual and social functioning deemed permanent.

Sharing his successful claim, Paul mentioned: "We've just received an email from our council, confirming a refund of £19,593. This is backdated to May 2007 - the year of our son's 18th birthday."

MSE suggests that countless individuals might be unaware that they qualify for the SMI council tax discount.

Anyone who is medically certified as having a severe impairment of their intellectual or social functioning, that appears to be permanent, may be eligible to a council tax discount.

Conditions like Alzheimer's disease, Parkinson's disease, serious learning disabilities, strokes, and other forms of dementia may result in severe mental impairment. For entitlement to the discount, the individual with SMI must also be receiving one of several specific benefits.

If a doctor has diagnosed you as severely mentally impaired and you live alone or only with others who are also severely mentally impaired, you will be exempt from paying council tax. Similarly, if you have been diagnosed as severely mentally impaired and you share your home with one other adult, your household will be eligible for a 25% discount on council tax.