Complex sentence: Mayor Boris Johnson chose not to stand for re-election for a third term in office, having been elected as the Conservative Party Member of Parliament (MP) for Uxbridge and South Ruislip at the 2015 general election.
Split into simpler sentences: Mayor Boris Johnson chose not to stand for re-election for a third term in office,. He had been elected as the Conservative Party Member of Parliament (MP) for Uxbridge and South Ruislip at the 2015 general election.