I am pretty sure it is Nick Lang. He also plays Umbridge's mom and Peter Pettigrew (not the rat).
Arthur Young - writer - died in 1820.
Arthur Murphy - writer - was born in 1727.
Arthur Murphy - writer - died in 1805.
Arthur Mathews - writer - was born in 1959.
Arthur Wilson - writer - died in 1652.
Arthur Wilson - writer - was born in 1595.
Arthur Bedford - writer - was born in 1668.
Arthur Bedford - writer - died in 1745.
Arthur Osborne - writer - died in 1970.
Arthur Osborne - writer - was born in 1906.
Arthur Young - writer - was born in 1741.
Arthur Groom - Australian writer - was born in 1904.