My change to the A10 yesterday was a big mistake. I misunderstood the "highway=trunk" tag. After I had done all the work, I discovered a comment on the wiki (osm.wiki/Talk:Tag:highway%3Dtrunk) that explains how this tag is used. As users TomH and Richard patiently explained to me, OSM's interpretation of "trunk" is not the same as the UK Highways Agency's definition.

I have undone all my changes. Apologies to anyone who was confused by the sudden change of the A10 from green to red and then back to green!

I'm going back to what I do best: making GPS tracks.