Complex sentence: In the United Kingdom, tellers are people working on behalf of political parties (usually as volunteers) who stand or sit outside the polling station and collect the electoral registration numbers (poll numbers) of voters as they enter or leave.
Split into simpler sentences: In the United Kingdom, tellers work on behalf of political parties (usually as volunteers). They stand or sit outside the polling station and collect electoral registration numbers (poll numbers) of voters as they enter or leave.