FAR Design Manoeuvring Speed is addressed at
eCFR :: 14 CFR 25.335 -- Design airspeeds. (FAR 25.335)
The relevant FTG is at
AC 25-7D, Flight Test Guide for Certification of Transport Category Airplanes
and, for the small brigade, a read through the relevant bits of the FTG at
AC 23-8C - Flight Test Guide for Certification of Part 23 Airports is time usefully spent over a coffee or ten.
I didn't check the EU story for this post but it should be somewhat similar.
The main problem (put into glaring relief post AA 587) relates to general misunderstanding of what Va is. The NTSB report at
In-Flight Separation of Vertical Stabilizer American Airlines Flight 587 Airbus Industrie A300-605R, N14053 Belle Harbor, New York November 12, 2001
should be mandatory reading for all aircraft pilots, both small and large certifications.
Post AA 587 the Industry undertook a significant training program to "unlearn" the general pilot misconceptions as to what Va was and was not. This is still ongoing, and slow, especially with the continuing retelling of the misconceptions in new pilot training. Being involved in such things in recent years, I do my bit but my voice is a voice in the wilderness, as it were. Others with a certification background do likewise but, sometimes, it all looks like a losing battle. On the small aircraft front, the problem probably will slowly go away as we see more aircraft move to the use of Vo in lieu of Va.