A number of military figures have criticised 'Frankie's Story', which aired last week, because the storyline centred on bullying in the army.
McNab has now added to the complaints in an article for The Daily Telegraph.
Writing from Afghanistan, he said: "Guess what, I haven't seen a single victim, idiot or bully yet. All I see, wherever I look, are soldiers getting on with the job... [Writer Jimmy] McGovern has been quoted as saying, 'As a dramatist I was interested in exploring how soldiers have to be of a certain mindset to kill'. But what McGovern has done, and the BBC allowed him to do, was ignore the first rule of writing - write what you know."
McNab suggested that McGovern should have spoken to soldiers before writing the episode, saying: "The families of those men and women conducting difficult and dangerous operations in Afghanistan were exposed to the lie that their son may be at risk to this kind of violence. The programme simply does not reflect the truth of what the Army is about... Of course the Army has its problems. Nowhere is perfect, but let us be clear - bullying has absolutely no place in the Army."
He continued: "What McGovern and the BBC have done is to use our armed forces as a platform to 'explore' something they know nothing about. In doing so, they have enraged those who serve and terrified their families back home. Our troops are fighting a war as professional soldiers, not victims, and the sooner everyone switches on to this fact, the better.
"We pencil-necks (civilians) must not think of our professional soldiers as victims. They are victors, not victims. They do not want or need our pity, just our understanding of what they do and why. Sadly, the BBC, our public broadcaster, has failed spectacularly to do its job and inform us of what we desperately need to understand."
The BBC's director of vision Jana Bennett has previously defended the programme, pointing out that it was a "piece of fiction".
Accused continues with a new story tonight at 9pm on BBC One.