Martin Lewis has branded the concept of Blue Monday – the so-called most depressing day of the year – a "piece of c**p".
The consumer rights campaigner wrote on Twitter: "Blue Monday is a piece of c**p pseudo science originally part of a travel company's press release to sell holidays.
"Can we all try to avoid rewarding marketeers, using this term, which tries to sell goods by parasiting on the back of real mental health campaigns."
Blue Monday is the name given to the third Monday in January which has been touted as being the most depressing of the year as a result of factors including weather, finances after the festive season, and return of a regular work routine.
The term was first coined by psychologist Dr Cliff Arnall in 2004 when a travel company asked him for a scientific formula for the January blues for one of their marketing campaigns.
Arnall has since admitted that Blue Monday is a "self-fulfilling prophecy" after so many companies jumped on the trend for the purpose of profit.
However, the label has stuck and now every January it is used by companies to promote deals that offer an escape from a mundane or stressful life.
Lewis' anger was echoed by national charity Samaritans, who suggested an alternative of "Brew Monday", where you talk over a cup of tea, should take over.
"We couldn't agree more!," they wrote. "That's why we're trying to get #BrewMonday to trend instead. Will you join us?"
And on its website the charity says: "Samaritans we know there’s no such thing as ‘Blue Monday’ – we all have our good days and our bad days, and those aren’t for the calendar to decide."
Using the Brew Monday hashtag, the official account NHS UK also wrote: "January can be a difficult month for many. Use today to reach out to a friend, colleague, family member or neighbour over a cup of tea. You could even try to have these catch ups on a regular basis."
Lewis and his supporters have looked to turn the Blue Monday phrase into one that encourages people to protect their mental health, and away from a commercial campaign tool.
By Monday lunchtime, his tweet had amassed more than 10,000 likes on the social media platform.
Mental health charity Mind previously founded the #BlueAnyDay hashtag to remind the public that one in six people struggle with depression at some point in their lifetimes and that the illness is not something to be trivialised.
“Blue Monday contributes to damaging misconceptions about depression and trivialises an illness that can be life threatening," said Mind’s head of information Stephen Buckley.
"One in six people will experience depression during their life. It can be extremely debilitating with common symptoms including inability to sleep, seeing no point in the future, feeling disconnected from other people and experiencing suicidal thoughts."