www.citizensadvice.org.uk/law-and-courts/discrimination/what-are-the-different-types-of-discrimination/indirect-discrimination/
Who does the practice, policy or rule affect?
The practice, policy or rule applies to a certain group of people in the same way regardless of who they are. For example, you could have a rule that all employees in a shop must work on Saturdays. This is a neutral rule which affects everyone in the shop. This group is called the pool for comparison.
Within this group, some people with a particular protected characteristic may be put at a particular disadvantage by the rule. For example, if you’re Jewish and observe the Sabbath, you can’t work on Saturdays. It doesn’t matter that there aren’t any other Jewish people who work in the same shop. It can still be indirect discrimination if something would normally disadvantage people sharing your characteristic.
Are other people disadvantaged?
You need to show that people who share your protected characteristic are also disadvantaged, but that the other people in the group to whom the practice, policy or rule applies aren’t.
How do you show disadvantage?
Sometimes, you can rely on common knowledge to show how some people are disadvantaged. For example, it’s common knowledge that Sunday is a day of worship for Christians. So a rule forcing staff to work on Sundays would put Christians at a particular disadvantage.
Sometimes, you may need to use statistics to show how people are disadvantaged by the policy, practice or rule. At other times, it may be necessary to use the help of an expert.
When might it not be indirect discrimination?
Indirect discrimination can sometimes be lawful. The Equality Act says it’s not indirect discrimination if the person applying the practice, policy or rule, can show there’s a good enough reason for it. They would need to be able to prove this in court, if necessary. This is known in legal terms as objective justification.
So i think if 100% of the men in the same job don't have a problem and the statistical % of the general population of males who are 5ft are vanishingly small compared to only 1 woman being affected by the policy change but women being reasonably common at that height, theres a clear case to answer.
It then comes down to whether the company has made reasonable adjustments or offered suitable alternative work.
Have they?
Offering an office job for lower pay certainly doesn't seem to cut it...