a. It was John who was injured, not Brown.
b. It was England which Brown lives in.
c. It was in 1993 that it happened.
All three examples involve it-cleft constructions. The usual punctuation convention is to not insert a comma between the matrix clause and its relative clause. For example:
- It was John [who was injured].
In the above example, the matrix clause is "It was John", and its relative clause is what is in italics "who was injured". Some grammar books will refer to that relative clause as an integrated relative clause.
(ASIDE: Instead of the term integrated relative clause, some of the older grammars use the older term restrictive relative clause. The use of the term restrictive relative clause can often be misleading, for that kind of relative clause does not always have a restrictive kind of functionality.)
In an it-cleft, the relative clause does not have a restrictive kind of functionality.
In general, the it-cleft's relative clause is used to hold the background info, while the matrix clause is used to foreground the important info. For example:
- b. It was England which Brown lives in.
The important info is "England", and it is foregrounded via the matrix clause. The less important info is backgrounded via the relative clause (since we can usually assume that Brown does live somewhere, and so, that info can be backgrounded, that he lives somewhere). A corresponding canonical type of clause could be "Brown lives in England".