It's rather late in the year to be doing any planting but hardy plants that have been grown outdoors (rather than in polytunnels) generally tough it out. I bought these two Hellebore foetidus and a pot of Arum maculatum at a market last week so I'll pop them in the ground.
 It's chilly but we haven't had a frost yet in inner London. In effect the big city has an extended growing season being a microclimate that is generally several degrees warmer then the surrounding region.