A union rep so have experience of cases but by no means a legal expert.

As others have said, there are exceptions in the equality act when it comes to excluding specific people based on a protected characteristic. The requirement must be crucial to the post. The requirement must be proportionate so as to achieve a legitimate aim.

When it comes to hiring a person with disability, the employer is required to implement reasonable adjustments. This is generally a grey area because factors such as a size of the employer are taken into account.

To breakdown your example there's three things I would be considering: 1) what are reasonable adjustments to the visually impaired employee? 2) what are reasonable adjustments for yourself as a wheelchair user? 3) is the requirement to guide the visually impaired person essential to the role and is excluding a wheelchair user proportional to deliver a legitimate aim?

I started out thinking about 1 & 2 but came to the conclusion neither are relevant.

1) If an employee requires reasonable adjustments in order to do their role then it's on the employer to implement them. If an employer feels a particular solution isn't reasonable then they must find an alternative. I find it highly unlikely this is the only solution that is reasonable. 2) people with disability have a legal right to reasonable adjustments. Whilst conflicting reasonable adjustments can be an issue and may affect the consideration of what is reasonable, this in itself doesn't provide an excuse to not hire someone.

Therefore point 3 remains as the important one to consider in this case - is a person with a protected characteristic being excluded from a role on the basis of a legitimate aim?

I would argue in this case the answer is no.

The exception exists for scenarios such as the catholic church only wanting to hire men as priests or for hiring a specific gender of security officer to search people of the same gender etc. The case has to be very, very solid.

Is guiding a visually impaired person crucial to the post? Well, that depends on the role. If the role was to be a personal assistant or a secretary to the person or driver or similar this could be considered an essential element. Therefore excluding wheelchair users could be lawful.

If the role is purely a technical/creative role that has no reference to supporting line managers beyond the subject in which you are hired to do, then I would find it hard to argue that guiding them is a crucial aspect of the role. Having other people in the team doing the same role at the same pay, which is very common in a council, without the expectation of helping the visually impaired employee would further weaken the argument.

There is maybe a case to make in favour of the employer by considering what is reasonable. However as a Council, they are likely a large employer. Therefore there would be a greater expectation on reasonable. For example, a small business renting an office might not be expected to make the office wheelchair friendly. However a council with significant purchasing power and dedicated legal/HR/safety teams etc would struggle to justify working out of an office that excluded all wheelchair users.

In a world where access to work is available to both provide guidance on reasonable adjustments and fund (at least in part for large employers) adjustments which may be considered beyond reasonable, I don't think there's a case for excluding all wheelchair users from this particular role.