The High Pay Center average masks a huge range in executive pay across the companies that belong to the benchmark FTSE 100 index.
Nearly half of the companies pay their CEO 100 times their average employee wage, and some several times that.
Martin Sorrell, the boss of the advertising company WPP(WPPGF) earns £29.8 million, 780 times his average employee.
At the other end of the spectrum are retailer Sports Direct,(SDISY) with a ratio of just 10, and 3i Group at 16 times.
The research is based on annual pay reports published by the companies, and average employee pay for each firm calculated by Pensions and Investment Research Consultants, which advises institutional investors on corporate governance issues.
The High Pay Center has called on the British government to cap executive pay at a fixed multiple of a company's lowest paid employee.
-- Editor's note: An earlier version of this story referred to the average CEO-to-worker pay ratio as 143 times. The High Pay Center has since amended its numbers.