Please answer a question about the following article about London:

London has a diverse range of peoples and cultures, and more than 300 languages are spoken within Greater London. The Office for National Statistics estimated its mid-2014 population to be 8,538,689, the largest of any municipality in the European Union, and accounting for 12.5 percent of the UK population. London's urban area is the second most populous in the EU, after Paris, with 9,787,426 inhabitants according to the 2011 census. The city's metropolitan area is one of the most populous in Europe with 13,879,757 inhabitants,[note 4] while the Greater London Authority states the population of the city-region (covering a large part of the south east) as 22.7 million. London was the world's most populous city from around 1831 to 1925.

As of mid-2014, London's population forms what percentage of the entire United Kingdom population?
12.5