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Top bosses will have earned more money by the end of Tuesday than the average worker will do in a year, campaign group the High Pay Centre has claimed.

The group has declared the day Fat Cat Tuesday, based on FTSE 100 chief executives earning £5m a year, compared with the median UK salary of £27,645.

The think tank says its aim is to highlight the "unfair pay gap".

The calculations were criticised as "pub economics, not serious analysis" by the Adam Smith Institute.

"None of these complaints are valid unless the High Pay Centre thinks it has a better way of estimating the value of executives to firms than those firms themselves," said the institute's executive director, Sam Bowman.

"The High Pay Commission's complaints only make sense if you assume firms don't actually care about making money - which is to say, they don't make sense at all."

12-hour days

The High Pay Centre's estimates are based on chief executives working 12-hour days and taking few holidays, giving them an average hourly pay of £1,260 an hour.

At this rate, it means bosses only need to work 22 hours - taking them to Tuesday afternoon, assuming they started work on 4 January - to reach the median full-time employee salary.

The body uses a mean average for chief executive pay and a median average for workers' pay, which means the figures are not directly comparable.

Nonetheless, High Pay Centre director Stefan Stern said its figures raised doubts about the effectiveness of government efforts to curb top pay.

"Overpayment at the top is fuelling distrust of business," he said.

High executive pay has been in the spotlight since the financial crisis.

Since 2013, UK-listed companies have had to publish a single figure detailing their top executive's salary, as well as being required to give shareholders a binding vote on directors' pay.

The High Pay Centre is calling for further measures to be taken, such as representation for workers on company remuneration committees that set executive pay, as well as publication of the pay gap between the highest and median earner within a firm.