texture aliasing and mipmap problem

I am quite new to Unity and am having basic issues with my textures. I have a huge building that I have modelled at 1:1 scale. I am starting to bring in the various elements of the building a bit at a time to learn the basics of Unity and how to apply reasonably basic textures.

The building is made of profiled metal cladding. I have made a normal map in NDO at a 2049x2048 resolution. This has been applied to a new material in Unity and put onto one of the walls. I have told Unity that the texture map is a normal map.

By default, the material looks 'ok' close to the camera, but it seems to get very bad at distances away from the camera. There are clearly 4 'steps' in the quality, with the fourth and most distant step having no apparent texture (normal map) applied. My scene looks like this:-

I played around with a few settings of the texture and unchecked 'Generate Mip Maps'. Whilst the texture now doesn't fall away in these abrupt steps, the aliasing of the texture is terrible, as can be seen here:-

There must be some setting somewhere to sort this out. I'd imagine I will find the same issue with any repeating texture: brick walls, paved floors etc.

Please could you offer some advice as to where to start looking?