Right so I watched the fourth episode again, this time sober
Anyway re the identity of the 'spy'?
There were five of them all named after the romantic poets and 'Keats' was a couple I think because BR refers to them as 'they' meaning more than one so Keats was a couple or at least two people so maybe even a family.
Bill Raggett or Robbie Platt was Blake.
Byron is a clue so he must be involved the pheasant was killed on the lawn at Byron's country pile and the NUM lawyer met the two police detectives there so massive clue from Scott and Raggett also wasn't Keats.
Helen St Clair I don't think is the spy because although she said that Salisbury knows her real name (he doesn't) she also said that when someone looks into her file then she's informed by people looking after her safety so possibly on a witness protection programme.
All of the spies had been given alternative identities and they used the names of dead children so it would be easy to check who the spies were by checking their names which would be that of a long dead child.
So there's four spies left Byron, Coleridge, Wordsworth and Keats, Raggett texted all of them before he topped himself.
I still think Ian St Clair is one of the spies possibly Keats and a relative, maybe his wife?
There's a huge clue in the poem quoted by Raggett I think.
Tony