Labour party leader Jeremy Corbyn has gained momentum during the election campaign and regularly attracts big crowds to his rallies.
The kind of incidents reported include a bomb threat received by a Muslim school and racist graffiti.
British police said they arrested two more people during raids in connection with the suicide bombing at a Manchester concert.
We can confirm we have arrested a 23-year-old man in South Manchester, the police said.
Here is what we know so far about the attack, which was the deadliest in Britain since 2005.