It's the 1956-set drama that is peppered with such 2011 expressions as "Note to self", "Farting about" and "You just don't get it". Now the scriptwriter of The Hour has conceded that it contains exchanges that might "take the audiences out of the drama", which was trailed as one of the TV highlights of the year.

"When a line of dialogue jars and is seen as an anachronism, one holds one's hands up," said Abi Morgan as the six-part BBC2 series approached its climax tomorrow evening, adding that there have been moments that "haven't worked".

Sold in the build-up to the opening episode as a British version of Mad Men – a comparison that critics widely dismissed as invalid when the series actually began – The Hour is a thriller set in the world of fledgling television news in which the generally admired attention to period detail has not extended to the dialogue.

Morgan, whose other credits include the script of the film version of Monica Ali's Brick Lane, and who has scripted the forthcoming Margaret Thatcher biopic The Iron Lady, was responding to charges of linguistic anachronism from those who had hoped that the language of the era would be as lovingly recreated as the The Hour's stunning sets and costumes. Blogs and comment forums have been filled with examples of jarring phrases that would never have been uttered in the 1950s.

In one scene, leading character Freddie Lyon, played by Ben Whishaw, was said to have "bottled it", a phrase not recorded by the Oxford English Dictionary until 1979. A complaint about one's "commute" would not have been heard in 1956, language historians say. Nor at that time would anyone have talked about "going for a Chinese". Other instances cited include the use of "reference" as a verb, and the expression "I'm on it".

"It is aesthetically offensive to anyone who cares about accuracy," says cultural commentator Norman Lebrecht. "A key line in the opening episode which was intended to establish a character was just wrong. Hector wouldn't say 'I'm a big fan of yours' – it is an Americanism, it just leaps out at you as alien to the period. The jokes are not 1950s, the word play is not word play drawn form the lexicon of the period."

Lexicographer Jonathon Green, author of Green's Dictionary of Slang, said: "The Hour has a big banner out saying this is a presentation of the BBC as it was in 1956 and you owe it to your audience to get the language right and not use phrases 20 years too early."

Explaining her approach to scriptwriting, Abi Morgan said in an email to The Independent: "I approach writing a period piece as I would approach all my other projects, focusing on the truth of the characters' journeys but primarily it is a fictional world. The past is another country. I write as an intrigued foreigner inspired by a new landscape. But I am a dramatist. I elaborate. I imagine. I tell a story. And hope it will be enjoyed. When a line of dialogue jars and is seen as an anachronism, one holds one's hands up. But more because it has taken an audience out of the drama. The Hour is escapism and for that moment the escapism hasn't worked."

Morgan's script, however, was defended by Deborah Cameron, Professor of Language and Communication at Worcester College, Oxford. "The speech given to characters has a different function from the costumes they wear, their hairstyles or the design of the set," Ms Cameron said. "With dresses and chairs and cars, period detail is important: it's the way you create the illusion of authenticity. But the dialogue is primarily there to convey information about character and situation, and an obsession with avoiding contemporary ways of speaking would not be helpful for those purposes. It would sound mannered and therefore inauthentic."

Morgan has taken another risk, it seems, with The Iron Lady, in which Meryl Streep plays Lady Thatcher. After an advance screening, friends of Lady Thatcher were quoted in the Mail on Sunday yesterday expressing their dismay at the way she was portrayed. Morgan's other big upcoming release is the long-awaited film version of Sebastian Faulks's First World War novel Birdsong.