I am the worlds expert on running when work gets too hectic - I've been on that hampster wheel for the last 3-4 months.
Firstly, don't beat yourself up if you can't run sometimes there are other priorities that need to be attended to.
Secondly, make sure your weekend runs count (if you're not working weekends!) by doing one long run and one hard session.
Third, never assume that you won't be able to run. Always have running kit close by - you never know when you'll be able to slip a qick one in (oooh, suits you sir!)
Four, 20 minutes of running (with 10-15 at a hard pace after warm up) is better than none at all.
Five, try running in the morning to get it out of the way before the day starts.
Six, buy a treadmill or ask you boss to buy a treadmill for work that way you won't mind training at unsociable hours.