I found this talk by Prof. John Robson to a Canadian Libertarian group on Magna Carta to be very enlightening.

https://www.youtube.com/watch?feature=player_detailpage&v=THaIFWYWms8

He has a nice opening with Alfred and the cakes. His talk stitches Magna Carta into the history of the Anglosphere.

This talk by Daniel Hannan given at Runnymede in 2013 is also very interesting

http://magnacartadocumentary.com/daniel-hannan-on-magna-carta/