The disparity in pay between those at the top and bottom of the earnings ladder is revealed by analysis showing the national minimum wage would be £5.24 an hour higher if it had risen at the same rate as a FTSE 100 chief executive’s pay over the last two decades.

With 2018 marking the 20th anniversary of legislation that heralded the minimum wage, research by the GMB union underscores by just how much the statutory pay floor has failed to keep pace with executive earnings.

It shows that if increases in the national minimum wage had kept pace with a chief executive it would be £12.74 an hour compared with £7.50 now for those 25 years and older. For a worker aged over 25 on 40 hours per week this would equate to £26,000 a year compared with the £14,664 they are currently paid.

The national minimum wage was a hugely important step for working people in this country and its anniversary should be a cause for celebration of how far we’ve come

The disclosure will intensify the debate about the yawning gap between the best and worst paid. Analysis published last week by the Vlerick Business School, based on 2016 data, found that chief executives of FTSE 100 companies receive on average 94 times more than the average employee. The average FTSE 100 company chief saw an 11% rise in their median total pay between 2015 and 2016.

Calculations by the High Pay Centre confirm that the average FTSE 100 chief is now paid £4.35m a year – compared with £1.23m when the national minimum wage came in – an increase of 354%.

“The national minimum wage was a hugely important step for working people in this country and its anniversary should be a cause for celebration of how far we’ve come,” said Tim Roache, GMB general secretary. “But this 20th birthday risks being marred by the growing pay gap between workers and company bosses.”

Every year the High Pay Centre highlights “fat cat day” when the average FTSE 100 chief executive will have already been paid the same as the average UK worker earns in a whole year. In 2018 the day falls on 4 January.

Stefan Stern, director of the High Pay Centre, said: “It’s striking that the national minimum wage came in just as executive pay really started to spiral up and out of control. The pay gap has grown ever since, with terrible consequences. There are two ways to close this unacceptable and unjustifiable gap: one is to have more restraint at the top, and the other is to have the long overdue pay rise that lower paid workers deserve. We need rapid progress at both ends of the income scale.”