What important event took place in London on May 7th, 2020?

On May 7th, 2020, the important event that took place in London was the London Mayoral Election. This election is significant as it determines the mayor responsible for governing Greater London, overseeing various aspects such as transport, policing, housing, and environmental policies. The mayoral elections occur every four years and are a high-profile event within the city's political calendar, affecting millions of residents.

While other events listed might seem significant in their own right, they did not occur on that specific date. For instance, the House of Commons elections typically wouldn't coincide with the mayoral elections, as those are held at different intervals. The London Marathon is a well-known annual event, but it was postponed in 2020 due to the COVID-19 pandemic, and the Trafalgar Square Festival is generally a summer event, not linked to May 7th. Thus, the mayoral election held on this date stands out as the key event.