This is the article that appeared in the Daily Mail on Saturday, but seemingly only in Scottish editions. It quite categorically states that Karen Gillen is playing Neil Gaiman and Todd McFarlane's character Angela in the new Guardians Of The Galaxy movie. It was then picked up by the tabloid Scottish paper, the Sunday Mail, which has no relation to the Daily Mail. However, the article doesn't appear on the Daily Mail or the Sunday Mail websites.
They do quote a Marvel insider… but it does rather smack of something just made up. I am reminded of when the Daily Mail quoted a Buckingham Palace source over the appearance of a revived mutant Princess Diana in Marvel's X-Statix that caused such kerfuffle at Marvel. And it took Marvel months to conclude that the Mail hadn't actually had a Palace insider at all and probably just made up the quotes printed.
I reckon that the paper picked up on internet speculation – which, lets face it could be true, as Karen Gillan playing Angela in a Guardians movie does make some kind of sense – and then turned it into an article in a desperation to run anything with Karen Gillan in because their readers like her. And she's Scottish. And they can suggest she's going to get her kit off.
Then they got someone who works in comics – possibly even just works in a comic shop – to be a "Marvel insider". Which was enough to bolster the original rumours, even though we're basically just listening to an echo chamber.
Also we'd really like to see this Clara: The Impossible Girl episode of Doctor Who that the Mail believes Neil Gaiman wrote.