Your local router, the cabinet near your house, has too many people connected to it.....oversubscribed UBR, is the name for it, and will probably take weeks for them to do anything about it....and as soon as they increase capacity, your on a countdown until it becomes congested once more...
I don't believe that, mainly due to the fact about a month ago, we had a VERY long extended downtime due to some building contractor up the road, long story short, virgin had to fight to get access to their cable back, and all of my area went without broadband,tv and phone for like 3 weeks i think it was. During that time sky poached a lot of people(tried to poach me but didn't work, and i already noticed he had 87 people on a list already).
So if anything they are severely under-subscribed here, would also explain why they keep offering me deals (even though i have the best service possible with them -.-). But I've rung them up and they are gonna send a engineer around tomorrow to have a look.