I lifted all the remaining potatoes last Sunday. Disappointingly, the printed labels that came on each pack were not weather-proof, so the experiment to find out which varieties worked best was slightly hampered. Best guesses though:
ColleenMatured earliest, first row lifted in early July, but a noticeably larger potatoes a month later. Good number, and even but not excessively size. Virtually no pest damage.
OrlaVery low yield in number, only 2-3 per plant, but very good size. Bigger than any of the other varieties by a big margin, would make good baking potatoes despite being an early variety. Very little pest damage.
Milva and ValorThese are the two I'm not sure about, which is a shame because of the difference in results. Both yielded about the same, reasonable numbers of potatoes but a bit on the small size - not unreasonable as they are main crop varieties and shouldn't be lifted for another month but the foliage had died down so they weren't going to grow any bigger. One of the varieties showed virtually no pest damage, on the other about 50% of the potatoes had holes, presumably from slugs as there were still a few in residence.
RobintaBest yield of all, although none were very big. Again, this is a main crop variety and should have continued growing for another month or so. In general very little pest damage, but a few that ended up in the middle of an ants nest had some surface damage - hardly surprising!

In conclusion, fairly pleased. Including the row I lifted in July, probably about a sack in total. This was on unmanured ground, big sticky lumps of waterlogged clay when planted, which had just been cleared of weeds for the first time in years. Another plus point is no problems with blight or other diseases, despite other plot-holders being affected this year. A bit of a puzzle why the main crop foliage died down so early, they were kept watered during the dry spell.
Next year, I think I will buy larger packs of Colleen and Robinta.