Mushroom,
This is certainly an atrocity, but was it carried out on the orders of Islamic State, or the act of a madman? Blaming IS or letting them take 'credit' when there isn't any proof is a mistake. Just because IS says it was their work is not proof that it was.
From the information that is in the public domain now, the killer is described as 'not normal' and unislamic in that he didn't go to the mosque, he drank alcohol and ate pork. He was a criminal with a record for violence.
If more information is made public, and a connection is made to IS, then I may change my assessment. But at the moment it looks to me like the act of a madman with a grudge rather than a jhadist.
I expect we will know soon which it is.
Funny you should mention the Birmingham Six. That was a case of the wrong people being blamed.