Complex sentence: His grandfather was Frederick Kisch, the highest-ranking Jew ever to serve in the British Army, and he held British citizenship until having to renounce it in 2015 as a condition of being allowed to take up a seat in the Knesset.
Split into simpler sentences: His grandfather was Frederick Kisch, the highest-ranking Jew ever to serve in the British Army. He held British citizenship until having to renounce it in 2015 as a condition of being allowed to take up a seat in the Knesset.