Couple of comments:
Firstly, I have an undiagnosed eye/balance/brain malfunction going on, which means I'm slightly unsteady on my feet and easily confused (but hey - that just makes me an 'artist'). Shooting figurative stuff - my serious snaps, inasmuch as any of them are serious, horizons really dont matter and I haven't noticed many unfortunate wonks. But I carry a d*g*t*l pocket camera when travelling (Paris yesterday) and many of my urban street shots are on the wonk. With my usual arrogance, it had the be the stupid camera - perhaps some idiot didn't stick the sensor in place straight. Change camera. Funnily enough, the same idiot sensor sticker-on chap had moved factories and I had another camera from a different manufacturer, but sensor attached by the same bloke and this, too, was on the wonk. What are the chances of that? Perhaps it was me after all.
So, when shooting urban, the camera has to be level with the ground and perpendicular to the ground and perfectly perpendicular to the subject, if photographing a wall, otherwise the mortar joints, which are usually pretty straight, will be on the wonk. Without a tripod and a great deal of messing around, I would suggest that it's pretty difficult to handhold a camera in all 3 dimensions without wonk. Then there is barrel distortion, glass anomalies... The other difficulty is your particular lens; a 400-anything is very hard to control. The slightest deviation could be amplified. Depending on the distance of the subject relative to the camera, it could be very difficult to try and get all 3 axis points aligned.
The point of all this ramble - try and light 135 35mm or 50mm lens in a town and see how you get on with the angles reading true. All my urban horizons fall to the left.But if I try and compensate for that, I go too far the other way. But it's a good illustration of muscle restriction etc, without the weight of a 400 lens, which may not be the lens of choice for medical folk.
Lastly, we are often too critical of our own work. As you are in the UK, the next time you watch the BBC or C4 news and there is a report from parliament, have a look at the verticals - Westminster is falling down. But because the pictures are moving and we are supposed to be looking at the reporter, that's considered OK & industry standard. If a dedicated FW took the same snap, we'd bin it and consign ourselves to a physio, go to Specsavers or, probably, head to the nearest camera shop to fix the problem.
