Complex sentence: As mentioned above, Labour majorities since 1935 have been substantial meaning the area is potentially one of that party's safe seat's, in 2010 the closest runner-up was from the Liberal Democrat candidate.
Split into simpler sentences: As mentioned above, Labour majorities since 1935 have been substantial, meaning the area is potentially one of that party's safe seats. In 2010 the closest runner-up was from the Liberal Democrat candidate.