April 28 (Reuters) - S&P:
* S&P says ratings on the United Kingdom affirmed at 'AA/A-1+'; outlook remains negative
* S&P says affirming long-term sovereign credit ratings on the U.K. at 'AA'
* S&P says Brexit continues to present a significant risk to U.K.'s track record of strong economic performance
* S&P on U.K. says outlook remains negative, reflecting continued institutional, economic uncertainty surrounding brexit negotiations
* S&P says Brexit continues to present a significant risk to the U.K.'s large financial services sector in particular
* S&P says "we also see a heightened risk to external financing conditions in light of the U.K.'s high gross external financing requirements"
* S&P says affirmed the 'AA/A-1+' long- and short-term issuer credit ratings on the Bank Of England
* S&P says U.K. has "prospered" as EU member and subsequent deal with EU will likely not be as beneficial for economy as full membership
* S&P says outlook on the long-term rating on the Bank Of England is also negative
* S&P says "we further think Brexit will continue to create challenging political and constitutional issues around the unity of the united kingdom"
* S&P says despite forecast for slight narrowing of current account deficit, still view U.K.'s high external deficits as vulnerability
* S&P says view the U.K.'s monetary and exchange rate flexibility as a key credit strength
* S&P - given uncertainties around Brexit negotiations, expect GDP growth in 2017-2020 to average 1.4%, down from pre-brexit forecast of average of 2.1% in 2017-2019
* S&P says could lower the rating on U.K. if GDP per capita (in U.S. dollar terms) or public finances weaken markedly beyond S&P's current expectations Source text (bit.ly/2oTvw3T)