Paul, I don't have a desk job but have been a student for a few years and have used the computer quite regularly. Actually, when I first started noticing the tension I attritubuted it to computer use because my left shoulder side rises upwards when leaning down on my right side using the mouse.
If you've been a student recently, maybe carrying around a bag could've also caused problems. That happened to me thanks to carrying books around for ages in a back pack & only using one shoulder strap.
I had been wondering as some of the other posters commented that it is normal to have more tension on one side of the body. When I sit in half lotus one side is definitely more tense than the other and switch sides every session to try to have a balance.
I had a long conversation about posture with a monk a few weeks ago and he said that it's going to be the case that one side is a bit easier than the other when it comes to stretching into a meditation posture. I sit Burmese style and one leg always feels more comfortable when next to my thigh than the other. I guess everyone's a bit wonky.