Action precipitated by an RA is mandatory and trumps any other ATC instruction - it has to be, otherwise you're kind of defeating the object of TCAS.
DS raises some valid points, which are only going to get worse with the ever-diminishing airspace available in and around the UK. Most other nations have dedicated Mil airspace that civ traffic does not fly through - at least routinely. Then again, most other nations have the space to do so!
One possible option here is for civ traffic operating OUTCAS is to operate in TA only - it would avoid the scenarios described above and doesn't present any real additional risk - after all, ALL players were operating in this fashion until only a few years ago. The TA mode would simply give you some additional SA that you didn't have before, and let you make the decision on whether avoiding action was warranted - which it generally wouldn't be.
Persuading your company to incorporate that into their SOPs may be the hardest part of that battle, though!