Ex-spy Katharine Gun -- the lead character in the new movie "Official Secrets" -- believes the dramatisation could also damage the partially repaired reputations of the UK and US leaders behind the military action.

Former British premier Tony Blair and US president George W Bush were dogged by criticism for years after launching a conflict that ultimately killed hundreds of thousands of people.

But in recent years they appear to have been able to move beyond the issue.

"This film might go some way to redressing that -- let's see," Gun, a former intelligence translator, told AFP ahead of the screening at the London Film Festival this week.

The 45-year-old leaked a top-secret US intelligence memo in 2003 which requested Britain's help in spying on non-aligned UN Security Council members to win a key vote authorising war.

The revelations caused a political storm at the time and saw Gun, who eventually admitted leaking the document, charged with breaching Britain's Official Secrets Act and nearly end up in prison.

She and some of the film's creators hope the movie will highlight again that invading Iraq was justified on the false premise Baghdad had illegal weapons of mass destruction (WMD).

"There's no rehabilitating two leaders who have had to admit that the whole WMD thing was an absolute fabrication and a manipulation and a lie," said director Gavin Hood.

"It's terrible, this rehabilitation of George Bush only because (current US President Donald) Trump seems worse... We've got to stop this nonsense."

- 'Back to normal life' -

"Official Secrets", which opened in the United States in August and hits cinemas in Britain in October before being released elsewhere later in the year, chronicles how and why Gun leaked the memo and the fallout from it.

The British government eventually opted in 2004 not to prosecute Gun after she pleaded not guilty. It would have been forced to disclose key documents and decision-making related to the Iraq war.

A mum-of-one now based in Turkey, she and her husband remained living in the shadow of GCHQ, the government eavesdropping centre in southern England where she had worked as a Mandarin translator, until 2011.

"All I wanted to do was just to go back to normal life, and that's what I did," Gun said, who went on to work as a Mandarin tutor -- even coaching former colleagues from GCHQ.

"It took me a long time to come to terms with the events... every time I tried to recount (them), my stress levels would go up again."

Another central character in "Official Secrets" is Martin Bright, the journalist at The Observer newspaper who received the leaked memo and broke the story, and is played by actor Matt Smith.

"It was immensely exciting," Bright recalled of the experience.

"It's the journalist's equivalent of scoring a goal at Wembley -- getting a front page news story in a Sunday newspaper.

"I've subsequently felt that this is an extremely important story that risked being forgotten."

- 'Questions about loyalty' -

Gun said she was initially hesitant about getting involved in the film, fearing another false dawn after numerous failed attempts to make a movie about the dramatic events that have shaped the last 16 years of her life.

But after spending several days forensically recounting it all to Hood, a South African-born director whose other politically driven films include "Tsotsi" (2005) and "Eye in the Sky" (2015), both were convinced of the importance of the collaboration.

"I'm telling this story because I think it raises interesting questions about loyalty... to what and to whom do we owe our loyalty?" the director said.

People's loyalty should be to "fundamental values as espoused by the American constitution and its bill of rights and if you step outside of those, you don't have my loyalty."

For Gun, the film reminds audiences of the apparent lack of accountability for Bush and Blair over the Iraq War, which caused immense suffering and eroded regional stability.

She also sees a correlation between this and the prevailing political culture in Britain and the US, where Trump and British Prime Minister Boris Johnson are frequently accused of dishonesty.

"If they see that other people haven't been held to account, it sets an extremely bad example," Gun said.

"And human psychology says that you just emulate what you see."