Keygrip,
The 7110.65 (3-9-6 & 7)that we use in the US is very specific as to the proper application of wake turbelence.
3-9-6
e: NOTE: The pilot may request additional separation; i.e., 2 minutes vs. 4 miles, but should make this request before taxiing onto the runway.
f states: Separate IFR/VFR aircraft taking off behind a heavy jet/B757 departure by 2 minutes, when departing. A pilot can not waive the wake turbelence delay behind a heavy/B757.
3-9-7 a.1: Separate a small aircraft taking off from an intersection on the same runway behind a preceding departing large aircraft by ensuring that the small aircraft does not start takeoff roll until at least 3 minutes after the large aircraft has taken off.
A pilot may waive the 3 minutie delay unless it is a heavy/B757.
b3. basically states that for small aircraft in the pattern must maintain visual separation with the preceding large and be issued a " caution wake turbulence"
Mike
NATCA FWA