The next morning when I launched Steam to see if I could download what was another 20GB of data to complete the problematic update to a game (due to a dlc purchase) I found the download to be fast and stable.
Reading the various feedback on the web, the best i could glean is that it may of been a DDOS attack on Steam. However, I haven't found anything official to say that it was - not even a news story.
But reading around, it seems some of the servers in the US were OK and others as per the most of Europe were not. A mixture of far away places seemed to be OK, but their distance meant that downloads were naturally slow but still significantly better than the two Steam UK server locations.
Luckily I generally backup my games to an external Hard Drive via the Steam built in utility which does a good compression job - I think Bzip may be used. With some of the games around 50GB in size and not enough space to have them always installed, it saves time and avoids "pressure" on the ISP, if I want to reinstall one. Although the only caveat to getting the game/software installed quickly from your possibly old backup, is that it seems it must be brought up-to-date first before it'll run again, so you still need the Net to complete it anyway.
Edited by Vorlon (Mon 09-Oct-17 11:51:41)