Complex sentence: Obliged to appear as C.P. Grogan because there was already a Claire Grogan in the British actors'union (Equity), her breakthrough role was in "Gregory's Girl", in 1981.
Split into simpler sentences: Obliged to appear as C.P. Grogan because there was already a Claire Grogan in the British actors union (Equity). Her breakthrough role was in "Gregory's Girl", in 1981.