I see Ryanair at its recruitment fair in Manchester in February is making a condition of applicants that they must be the right to live anywhere in Europe because they require the ability to ask their staff to be relocated to any of their hubs as their base.

Providing their conditions are legal, a business can decide to employ who it likes, so if this is what they decide, that's all there is to it. If that ends up excluding British citizens without dual nationality, it's not their problem as long as they can get enough applicants.