The last time I wore casual work clothes during my commute was when I lived < 2 miles from home. That was in Norcal where the year round weather was mild. If I had a longer commute I'd wear cycling clothes as I tend to sweat no matter the temperature. My commute now is 9km one way and I carry work clothes in panniers.

My recommendation: wear Dockers-type pants and roll up the cuff. Other option: get those convertible hiking pants where they convert to shorts via zipper. Wear them in shorts mode on the ride, zip on the legs when you get to work.

On a related note: it took you an hour to drive to work and it's only 7 miles?