Illegal orders are not to be obeyed, end of! That was what I was taught at Sleaford Tech early 60's in Air Force Law lectures. I doubt very much if that has changed since, despite the subsequent change to Military Law. Catch-22 is of course that not only are they not to be obeyed but they must also be reported! Hence the extraordinary official MOD position as stated by tucumseh above (#4655), whereby refusing to make false record is an offence whereas ordering it to be done is not!
That is front and centre of this scandal and why Regulation and Investigation has to be removed from MOD interference and made independent of it and each other.