YoullLaugh
It's not so much that you can't extend the argument in the way you describe, it's that there is a strong and obvious defence, so no one would bother.
The point I was making was that it would be indeed be laughable to extend the argument in that way - and you have picked up on the fact that there would be a "strong and obvious defence" - in other words, the bank can argue there is an "objective justification" of their decision.
Where I do agree is not so much about the fact that we are dealing with a couple (which I don't think is relevant) as the point I made above - that the court may accept that the treatment was not because of maternity/pregnancy, but because of dipping below the threshold.
Then we are in agreement about the key issue. OP is not being discriminated against because she is pregnant. She is also not being discriminated against because of any assumption that as a result of her pregnancy/maternity she may not be able to meet the affordability criteria. That would be direct discrimination.
She is being discriminated against because she does not meet the affordability criteria. The reason is her reduced income, as a result of maternity leave. On the face of it, that is clearly indirect discrimination.
The definition of indirect discrimination is:
The use of an apparently neutral practice, provision or criterion which puts people with a particular protected characteristic at a disadvantage compared with others who do not share that characteristic, and applying the practice, provision or criterion cannot be objectively justified.^
The objective justification here is the affordability criteria. This is something the bank has no choice but to apply, and it is applied to all applicants equally at the time of the application.
OneTwoOrThree
The discrimination comes from using maternity pay, not salary.
They aren't looking at salary. They're looking at income and outgoings in relation to the affordability of the product you have applied for, at the time of your application - see above with regard to indirect discrimination.
BellCurve's experience is a perfect illustration of just how limited it is.
It is simplistic to argue that OP's drop in salary is a result of maternity pay, ergo she is being discriminated against because she is pregnant, and that is direct discrimination. But that's not the case, IMO. It is indirect discrimination, objectively justified.
The law reflects the society we live in, and sadly women still bear the brunt of the economic and social effects of pregnancy, maternity and raising a family.
Finally, I would just like to clear up any misunderstanding about my position here. I am as frustrated as anyone else by the limitations of the law.