I think the logic goes like this. Vanguard is a Helipad. So is Battersea. If the tide is out, they become Elevated Helipads. JAR-Ops 3 operators currently benefit (if they apply for it and it is noted on their AOC) for a Performance Class 2/Class 3 alleviation to permit operations to Battersea (I'm not so sure about Vanguard actually being a 'standard' Exemption) as an elevated helipad. However, in the not too distant future aircraft doing this will require a UMS. Blame JAR-Ops 3. I think I am correct in saying that, for example, the standard VEMD and associated system in the EC120 would be compliant. It's to do with monitoring of engine parameters and the sums for Probability of Failure. A full IHUMS will not be necessary.