US company Omnicom and French firm Publicis say they are combining in a "merger of equals" that will create the world's largest advertising firm with a value of more than $30 billion (£20bn).
The combined company will be called Publicis Omnicom Group and be jointly led by Omnicom CEO John Wren and Publicis CEO Maurice Levy as co-chief executives.
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Ukip leader Paul Nuttall also said he would want to get rid of Sharia courts.
Over 40,000 people picked up their packs to take part in the annual marathon in the capital.
The country's voters are concerned about security, the economy, and the 10% unemployment rate.