I will make it simple for anyone asking what Over Utilisation is.
Imagine a Golf Ball And A Hosepipe.
Virgin Media is the hosepipe and your connection is the Golf Ball when too many people are connected at once. The hosepipe used to be like the inside of a fairly decent sized pipe where your Golf Ball could move about easily and at speed.
The more people who connect to the Pipe end up having lots of Golf Balls all trying to get down the pipe at the same time, but due to Over utilisation, the Pipe starts to shrink in size, and you struggle to get the Golf Ball down the hosepipe which was once a larger pipe.
Only way round this, is if Virgin Media invest in new Fiber tech, or upgrade the system with larger cables, better switches etc, and until that happens, they will be plagued with Over Utilisation (OVER USE).