rotorcaptain
Everyone agrees we're responsible for our own rotorwash, but it might not be as simple as 'period'.
I don't know about England but I believe most states here have what's called contributory negligence. If a court here decided the R22 pilot was say 15% to blame for the damage for not securing his blades when the other helicopter was landing upwind in a strong wind (basic airmanship) then the compensation he'd get for the damage would be reduced by 15%.