July 2003. Dr David Kelly walks into woodlands. He remembers inspecting fragments of documents.

Ten months earlier: Downing Street press secretary Alastair Campbell consults Joint Intelligence Committee head John Scarlett while the Committee finalises a dossier setting out the case for war in Iraq. It claims that Iraq can deploy chemical or biological weapons in 45 minutes. Iraq, 1991: UN weapons inspector Kelly queries a factory's supposed production of baby food.

January 2003. Campbell requests another dossier to overcome public scepticism. Its use of an old PhD is criticised. Scarlett complains about changes to wording.

March. On his daughter's wedding day, Kelly sees news footage of coalition forces bombing Baghdad. Asim telephones from Baghdad. Eight years earlier: Kelly questions Asim about Iraqi weapons. Asim befriends and helps Kelly.

April. Kelly is warned to clear press contacts. Kelly tells Newsnight journalist Susan Watts that the 45-minute claim was a mistake. Rihab Taha, head of Iraq's biological weapons programme, has been captured. Eight years earlier: Kelly questions, and upsets, Taha. Returning to Iraq to find WMDs, Kelly is deported from Kuwait because of a Foreign Office visa mistake. He feels that nobody cares.

May. Kelly tells BBC Today journalist Andrew Gilligan about changes that meant the dossier did not reflect the intelligence services' view. Gilligan's colleagues criticise his methods. Filing his live report from home, Gilligan attributes to his source claims that the Government knew the 45 minute claim was wrong and wanted the dossier to be sexed up. In Basra, Campbell and Tony Blair speculate about the source. Watts records a conversation asking Kelly about Gilligan's claims.

June. Returning to Iraq, Kelly contradicts American reports that mobile labs produced WMDs. Five years earlier: Asim claims that Saddam destroyed WMDs, but Kelly vows to return to prove weapons exist and dismantle them.

Evidence has been destroyed. Kelly denies being the source of a newspaper piece on mobile labs. Kelly converted to the Bahá'í faith, attracted by its respect for truth. While MI5 investigate, Kelly is advised to admit being Gilligan's source.

Campbell demands the BBC apologise for Gilligan's claims. Gilligan alters his notes of Kelly's interview, and gives a transcript to BBC news management.

July. The Ministry of Defence tells Kelly he breached regulations on contact with journalists. Pressured by BBC news management, Watts refuses to name her source and denies that her report corroborates Gilligan's.

Kelly's account contradicts Gilligan's. Learning this, Campbell proposes leaking Kelly's name. His superior stresses Kelly's world-leading achievements in biological disarmament. Asked to list other contacts, Kelly does not mention Watts. Blair wants to state the source has come forward without naming Kelly. Campbell wants a clear win with the BBC.

Kelly tells his wife, Janice, that he is the source. The Financial Times guesses Kelly's identity, forcing the Press Office to confirm. Journalist Nick Rufford tells Kelly he will be named. For Kelly, this ends their long friendship. Kelly and Janice leave for Cornwall. Kelly believes he is being sacrificed as a distraction.

Kelly is reprimanded but cleared to return to Iraq. This will be withdrawn if his account is contradicted.

Kelly gives evidence to the Foreign Affairs Committee. Today staff and Number 10 watch on television. Kelly defends the dossier and says Campbell didn't transform it. Read a statement, Kelly denies making it, but Watts recognises her interview, wondering how the Committee got it and why Kelly is lying. Kelly doesn't believe he is Gilligan's main source. Campbell is unhappy with Kelly's testimony, but Gilligan is pleased, believing Kelly's testimony nullifies his contradiction of Gilligan's report.

The Committee obtained Watts' interview from Gilligan. Kelly knows he made a mistake, surprised by a question not related to his briefing.

Kelly rejects Asim's suggestion that the Americans destroyed evidence. Asim argues that Saddam's regime, for its own safety, pretended to have the weapons it had destroyed. Al-Qaeda now has access to weapons scientists, endangering London. Kelly believes he cannot return to Iraq.

Kelly receives more questions. Blair's Congress speech stresses Saddam's WMD threat, and Britain's readiness to fight alongside America. Walking into woodlands, Kelly sits by a tree, taking out pills, a bottle of water and a knife.

Separately, Blair's adviser and Watts hear the shocking news.