Forum member amelie found an article by Ken Follet which describes some of this thoughts and involvement with the filming of the mini series, The Pillars of the Earth.

You can read the article HERE.

Here are a few quotes from the article which mentions Matthew Macfadyen:

"Most thrilling of all is the cast of first-class actors, many of whom I have seen and admired before. Prior Philip is played by Matthew Macfadyen, whom I last saw as Prince Hal in Shakespeare's Henry IV at the Royal National Theatre in London."

and 

"In the makeup trailer, I sat next to Matthew Macfadyen, who was being made to look 70 years old in preparation for a scene set late in the story."

In the October issue of UK's Mairie Claire, Keeley admits that a recent guilty pleasure was a child-free, sneaky, romantic weekend with husband, Matthew Macfadyen near Budapest (Matthew is currently filming "The Pillars of the Earth" in Budapest).  Keeley states: "We visited the thermal baths and dined out in the hills". 

I hope they had a lovely time!