(Reuters) - Ratings agency Moody's on Friday cut its outlook on the United Kingdom's long term debt to 'negative' from 'stable', but maintained its 'stable' outlook on the European Union following the UK's vote to leave the EU. Moody's said the Brexit vote will bring about a period of uncertainty for the UK, with negative implications for the country's medium-term growth outlook. (http://bit.ly/28WJRHE) Moody's also affirmed European Union's AAA rating and the United Kingdom's Aa1 rating on Friday. (http://bit.ly/28SL6Y5) (Reporting by Jessica Kuruthukulangara; Editing by Savio D'Souza)