Complex sentence: UKIP continued to be widely seen as a single-issue party and in the 2005 general election--when it fielded 496 candidates--it secured only 2.2% of the vote, and 40 candidates had their deposits returned.
Split into simpler sentences: UKIP continued to be widely seen as a single-issue party. In the 2005 general election, when it fielded 496 candidates, it secured only 2.2% of the vote, and 40 candidates had their deposits returned.