formality - Subjunctive mood: 'was' usage after 'I wish' and 'if only'

SFX Magazine had declared the sentence below as follow: 1) STAR TURN, 2) BEST LINES.

• 
  

  I wish Bernard Cribbins was my grandad. Perhaps he would be willing to
  adopt?

  
  




• 
  

  Rattigan: “If only that was possible.”
  The Doctor: “If only that were
  
  possible. Conditional clause.”

  
  

Is 'was' after 'I wish', 'if only' and 'if' (in conditional clauses) colloquial?

Does it be used in formal speech and writing?

Answer

There's nothing wrong with the sentences you write. Some people (I believe teachers among them) consider the use of the form was after I wish, if only and if (in conditional clauses) colloquial and claim that it shouldn't be used in formal speech and writing. They claim that the "correct" form to use is were. The language, however, has its own dynamics and is used regardless of the rules imposed.