Complex sentence: Robertson was a leading figure in the SLP, along with Sillars, however, unlike Sillars he stood down at the 1979 general election, deciding not to contest his Paisley seat.
Split into simpler sentences: Robertson was a leading figure in the SLP, along with Sillars. However, unlike Sillars he stood down at the 1979 general election, deciding not to contest his Paisley seat.