Original sentence: Antisemitism in the UK Labour Party has been the subject of public debate for decades.However, allegations of antisemitism against the party increased since Jeremy Corbyn was first elected as Labour Party leader in September 2015, as well as by Naz Shah and Ken Livingstone under Corbyn's leadership of the party
Edited sentence: Antisemitism in the UK Labour Party has been the subject of public debate for many decades.However, allegations of antisemitism against the party vastly increased since Jeremy Corbyn was first elected as Labour Party leader in September 2015 alongside controversial comments  made by Corbyn, as well as by Naz Shah and Ken Livingstone under Corbyn's leadership of the party