I found several articles with background info on this new Netflix series in which Jeremy will be playing Anthony Eden. Seems like it's based on the play The Audience, which is now on Broadway starring Helen Mirren. Claire Foy will be (a young) Queen Elizabeth and Matt Smith Prince Phillip.

Two from Variety:
(from Nov 2014) http://variety.com/2014/digital/news/netflix-takes-the-crown-british-drama-series-set-for-2016-1201355446/

(from June 2015) http://variety.com/2015/tv/news/netflix-the-crown-cast-matt-smith-claire-foy-john-lithgow-1201523102/

And from the Independent (Aug 2015):
http://www.independent.co.uk/arts-entertainment/tv/news/the-crown-netflix-is-making-a-tv-series-about-the-queen-and-the-tag-line-is-hilariously-game-of-thrones-10463790.html

Unfortunately, none of them mention Jeremy.