From Anchor Butter to Malcolm Tucker - Peter Capaldi on 'going sinister'Peter Capaldi says there was a specific moment he realised his casting had transitioned from affable geek to bad guy. It was during an advert for butter.
Source: From Anchor Butter to Malcolm Tucker - Peter Capaldi on 'going sinister' (https://news.sky.com/story/peter-capaldi-from-anchor-butter-to-malcolm-tucker-scottish-star-on-going-sinister-13229901)