harvesting maincrop potatoes

My Setanta potatoes are still green and flowering but I am going away in September. If I am going to let them rest in the soil for 10 days I will have to cut down the foliage at the end of this week despite it being green. The only alternative is to cut down the foliage at the latest possible moment and leave them in the soil (in containers) until I get back but that might be December.
  It has been a strange year in my garden.
Maybe this cold weather will cause the foliage to die back in the next few days.