OP
Bobster
This is not a bad idea in the scope of things, I often drill, tap structural steel for numerous reasons and when we are talking 6mm maybe 8mm holes there is neglegible effects to the structural integrity ..... when you start popping out a 100mm hole then yes this is when you need a structural assessment report. Dont get the mindset of the H&S regs that have been fashioned from heresay and have no foundation.
I'm talking from personal experience.
I have seen structural steel split from 6mm holes before. Fine this building was put under abnormal vibration. The building the OP is working in will probably not be. You could say this makes my point invalid, I have never personally done it myself since.