Sphagnum papillosum
There are several publications and keys dedicated to the Sphagna of Britain and Europe. The most recent of these are listed on the Bryophyte identification page under Resources.
Sphagnum palustre
Blunt-leaved Bog-moss
Sphagnum affine
Imbricate Bog-moss
Sphagnum medium
Magellanic Bog-moss