I asked the ATC at Hawarden that when they forever refused our Police helicopter to depart due to wake turbulence. Their excuse was that they were legally obliged to make us wait the required amount of time. They refused to budge despite the fact that I could draw representative flight paths to show that we never got any where near the wake.
Never had the problem at Liverpool. A simple "request immediate departure" and we were cleared to go.
I should imagine it's because parallel runway Ops is 760m for wake turbulence. If the Fuga has just landed / got airborne you're stuck for 3 mins unless a local Risk Assessment can be argued to allow you to depart. But with 2 upside down heli's recently (Cambridge and Gloucester) where adjacent aircraft were in excess of the guidance yet still created a safety event it's a brave person to sign that one off.