The Mother Redcap was a name of a nearby pub frequented by newspaper staff in the days of when Renwick was working in a provincial newspaper as journalist.
When C.I. Speed is showing the photos of the potential assassins he shows 1 photo and states that the person in the picture is a suicide bomber. By the very definition of the term "suicide bomber" it is a 1 time only act & therefore it is not possible to say, in advance, that a person is a suicide bomber. It certainly would not be the modus operandi of any professional assassin, for rather obvious reasons.
The rolling end credits include the disclaimer "No animals were harmed in the making of this programme" which refers to the apparently electrocuted rat.
"Mother Red Cap" is also the name of an alleged witch who resided in Camden Town in the 1870's.
After Jason Tippet tells Maddy about the first death, he states that between 1947 & 1951, 5 more men were found dead at The Mother Redcap public house. When Maddy & Jonathan visit the former pub, she says that the 6th victim was Sir Michael Pritchet, QC. In 1951 the British Monarch was George VI & therefore Sir Michael Pritchet would have been a KC & not a QC, as QC stands for Queen's Counsel, whilst KC stands for King's Counsel.