London commemorates 20 years since city's deadliest terror attackbr br A national service of commemoration is held at St Paul's Cathedral to mark the 20th anniversary of the London July 7 bombings which killed 52 people. UK Prime Minister Keir Starmer and Mayor of London Sadiq Khan join victims' families and survivors for the service. On July 7, 2005, four homegrown Islamist extremists detonated suicide bombs on three underground trains and a bus across central London.