Vital intelligence used to justify the invasion of Iraq 10 years ago was based on "fabrication" and "wishful thinking", a new documentary claims.

A BBC Panorama investigation, broadcast to mark the 10th anniversary of the start of the Iraq War, suggests security services relied on questionable information, and dismissed others that were contradictory.

The war, which started on March 20, 2003, lasted more than six years, claimed the lives of 179 UK personnel and more than 100,000 Iraqis, and cost more than £9 billion. Combat operations ended in 2009 but a decade on the war remains unfinished business, with ongoing questions about the legality of the invasion, and the conduct of British troops.

Tonight's Panorama programme – The Spies Who Fooled The World – documents the chain of secret information that contributed to the decision to invade, including new testimonies from intelligence sources.

It tells how claims from a few sources that Iraq was manufacturing Weapons of Mass Destruction (WMD) spiralled into apparently sound intelligence used to justify the war.

The programme alleges that certain intelligence was relied on out of wishful thinking, with one source telling the programme the Iraq War was borne out of "choice" rather than "necessity".