Williams is most famous for his work on The Fast Show and as the role of Arthur Weasley in the Harry Potter films, it's rumoured that Williams is set to play the role of Rory's father (see on location picture below, his similar dress style to Darvill's character is something to be noted).
In a recent exclusive from BlogtorWho the first official promo picture was release for the new season (see top picture) alongside new guest star announcements:
New guest stars so far confirmed to star will include David Bradley (Argus Filch in the Harry Potter movies), Rupert Graves (Lestrade in Sherlock and alongside David Tennant in Single Father) and, as announced yesterday, Mark Williams. Series 7 will then see a dramatic turn of events when The Doctor meets a new friend. Prepare yourselves for thrills, adventures and dramatic surprises as the show builds towards its enormous, climactic 50th anniversary year. Fourteen big, blockbuster-movie episodes - each a brand new epic adventure featuring new monsters and some familiar foes as you've never seen them before.
Season 7 of Doctor Who is currently set for release throughout Autumn 2012. You can read the 7 things we want to see in the new series HERE.