Police are cracking down on troublemakers ahead of this weekend's Notting Hill Carnival.
About 500,000 people are expected to attend the Notting Hill Carnival
Metropolitan Police said they have made 108 arrests since May and sent 33 warning letters to people that officers think will cause trouble.
During the arrest police seized firearms, six kilos of cannabis, £15,000 in cash and £100,000 worth of stolen goods.
Metal detectors will also be used at stations to prevent knife crime.
More than 10,000 officers will be on duty at the west London event over the August Bank Holiday weekend.
Ch Insp Rod Charles said: "We have had a dedicated team since May this year focusing on people who may cause trouble.
"We have been sending out letters to individuals warning them that if their intention is to come to carnival to cause problems that we will take preventative measures to stop them."
About 500,000 people are expected for the main party on Monday and 200,000 on the children's day on Sunday.
Police urged anyone wanting to join in the fun to plan ahead and to keep themselves safe by sorting out their journey and meeting points with friends and family in advance.
They also advise leaving valuable and expensive jewellery behind, not carrying too much cash or credit cards and keeping up with the flow of the crowd.