My 2014 vintage M&S Cycling Chinos have been great for this job, but the fabric has just failed (rather spectacularly) around where the right hand edge of my saddle would go.
I've got the full length Humvee Trousers, but they are made of similar rustly material to the shorts, so can look a bit like overtrousers. I'm wondering if anyone's tried any of the stretchy style walking/scrambling pants? They look like they might work