[Sephiroth]

I've been on 20 Mbps for some years. In the evening, I experience exactly the same as you. You are potentially lucky, looking at the speed stats. If anyone in your family games, then the maintained upstream speed is a boon. It means there's no upstream congestion and your speed could fall to c. 1 Mbps and the game's fps won't suffer.

The speed tests suggest a degree of downstream congestion - people downloading stuff, in essence. You could be one of those people. It's likely to be local to you i.e. centred on your street (single trunk passing the houses) or street box (capacity back to the regional head end from several streets).

People with real problems are those who report (e.g.) 0.01 Mbps upstream and/or 1 Mbps downstream during peak times.

Virgin have pre-identified on their web site their peak times and the effect on performance. The advantage you have with the 20 Mbps upgrade is the higher speed during non-peak times and the higher throttle threshold (try saying that).

With the above information and that offered by Broadbandings, you can decide whether or not to report the matter to support. I haven't done so.

HTH.