Publishing gender pay figures for each job type is perfectly reasonable. Comparing a company as a whole is not.
Let's say you have 10 pilots (9 men, 1 woman) - each on £60k. You also have 10 cabin crew (9 women, 1 man) each on £20k.
There is Zero gender pay gap between pilots. There is zero pay gap between cabin crew. But magically the 10 men average £56k and the 10 women average £24k. Not because there exists a gender pay gap, buy because the men generally chose a career that pays more. Hardly the companies fault!