One of the few things that really p1zzes me off in this industry is pilots who take themselves too seriously. Flaps 5, I think that you might be one of those. There is plenty of time to go for a pee on an EDI LHR.
The "box" will have been set up, briefing will be standard (probably) RT is being monitored under active radar control, a/c is on autopilot and there isn't exactly a lot if hills around BHX area. What more is there to do?
As for dress, I see nothing wrong with top button undone with no tie. It looks a damn site better than top button undone with your tie hanging around your waist.
The original question was a valid one and has received some valid answers. A good discussion point.
Barcode and CRP5, god help me if I have to fly with you and the **** should hit the fan. If your colleague in the other seat came up with a reasonable suggestion that you do not agree with would your reaction be the same? I hope not.