Spyware:xarqi: Back on the subject of quality, rather than content, I've seen a small amount of coverage on Prime via DVB-S FTA since I can't get DVB-T. I too have noticed digital artifacts not normally present. Predominantly this is blockiness on object edges during fast transitions within a scene or more generally immediately after a scene change. At times it really is quite bad. I attribute this to one or both of two things: uncorrected errors in the data stream from mobile cameras, and excessive compression in the link from London to NZ.
Your assumptions are wrong. The blockiness on Prime is 100% due to Sky playing out a very low bitrate stream into the encoders that feed the local Optus D1 feed and the DVB-T feed.
This does not account for the flaws appearing only in video from London, but it does confirm that the same data feeds both DVB-T and DVB-S, so my DVB-S observation would support the OP's DVB-T one.