McDiarmid drawn to 37 Days script
Ian McDiarmid and Tim Pigott-Smith have said that the script drew them to their latest TV project.
The pair star in a BBC Two docu-drama which tells the story of the final 37-day countdown to the First World War
Ian, 69, known to millions as Darth Sidious in the Star Wars movies, plays Edward Grey, the former Foreign Secretary.
Tim plays Prime Minister Asquith in the drama, which will be shown over three consecutive nights and examines the catastrophic chain of events that took place in the final weeks before war broke out in 1914.
"When I got the script, I was fascinated because I didn't know much about those 37 days that led up to it," Ian said.
"It's extraordinary that it did happen in 37 days, like a gigantic boulder gathering force and sliding down the hill - and it was a slide into war."
The factual drama begins with the assassination of Archduke Franz Ferdinand of Austria and examines how war on Germany was declared merely weeks later.
It was the strength of the script that also attracted Tim, 67, to the docu-drama, which comes as the 100th anniversary of World War One approaches.
"I read the material and it was just superb, an absolute brilliant example of historical research that's been put together so well it does cross the line between documentary and drama," he said.
:: 37 Days airs on BBC Two over three consecutive nights starting on Thursday, March 6.