No doubt this thread will quickly descend into the usual debate about how unfair this is - and how those lost 5 minutes could make the difference between winning or losing a multi-million pound deal (as opposed to a text alert from the IT department saying that there was a power outage half an hour earlier) - but the bottom line is that, rightly or wrongly, at the moment these are the rules and the purser was upholding them.
I was on an LCY flight yesterday and someone was up out of their seat as soon as we had slowed down on the runway. He got targeted straight away.