the wild flower key by francis rose. covers 1600 gymnosperms found in Britain. pretty standard id book for undergrad and jobbing ecologists
I use Rose as well, but also the Collins pocket guide to wild flowers of Britain and Northern Europe, which is not quite as good as a definitive book, but the keys are a heck of a lot easier to use unless you know your plant anatomy in enormous technical detail.
To be honest I tend to use the Collins guide as my go to book, and Rose for confirmation.
Well the transverse spotting on the leaves rule out Early-Purple Orchid leading to the genus Dactylorhiza which is made up of the Marsh Orchids and the Spotted Orchids. Looking at the flower leads me to the two species previously discussed - Common Spotted and Heath Spotted Orchids. Deciding between these two species can be tricky and it is likely they hybridise although I'd still maintain that the plant in question is the Heath Spotted-orchid - Dactylorhiza maculata. This is due to the shape and size of the flower 'lips' but also because the markings on the petals are more like lines rather than dots.
I always find that I learn most when someone challenges my identifications, because they inevitably bring different past experiences with them, which I won't have shared. Inevitably you end up with your own sets of assumptions about things, which may only be locally correct. Also, if my identification is open to challenge in the first place, it means I'm not entirely certain, so I could do top learn a bit more anyway.
Harvestman
Basically, if only nature would conform neatly to the categories we try to impose on it...
Oh yes, and many thanks to Mick721, not only for listening to us squabbling about identification, but for taking the trouble to post more pictures. It has been an interesting thread.