Blue Monday could be most depressing ever because of celebrity deaths, anxiety over Brexit, and fears about a Donald Trump presidency in the US, the expert who coined the phrase has warned.

In 2005 Dr Cliff Arnall, formerly of Cardiff University, came up with a light-hearted formula for predicting the gloomiest day of the year based on factors including weather, debts, time since Christmas and motivation.

His equation suggested that the third Monday in January – this year on Jan 16 – was when unhappiness peaked as Christmas bills roll in and the post-holiday buzz wears off.

But Dr Arnall said that this year could be even more depressing than usual because of Trump and Brexit anxiety, and sadness following the recent deaths of childhood heroes such as George Michael and Carrie Fisher which reminded people of their own mortality.