Well, that's the beauty here, in that it's a regular dog walk for me! and I can return for another look.
They are certainly late for (Common) Solomon's Seal round here. They are quite common in all the local woods, and have been in flower for a month now.
The purple stem has thrown me to be honest.
Reading up on the other Polygonatum species, Angular can have a purple stem, and flowers slightly later(?) but is very rare here.
Looks like hybrids have occurred not too far away.
Violet Helleborine was my only other thought, but that would be equally rare, if not more. (That is a 1 hour drive / twitch for me!). They do tend to grow in clumps, in their favour compared to other Helleborines.
Looking at the Orchid thread, the Dune Helleborine has a similar look too., (although not a contender down here). However, Broad Leaved (more likely) and Green Flowered (less likely) can both show purple stems.
Exciting, whatever it is.. It was very close to a well walked area, difficult to shelter it from feet (Human, Dogs, and Horses!), so let's hope we get to find out in a month or so.