The United Kingdom held onto its AA credit rating from Standard & Poor's Friday, but the agency cautioned that the country's Brexit negotiations would reduce investment, limit growth and potentially diminish the role of the pound as a global reserve currency.

S&P maintained its 'AA/A-1+' grade for the U.K., the third largest economy in Europe, but made no changes to the negative outlook. Britain lost its triple-A rating with S&P on June 27, just days after the country voted to leave the European Union.

S&P said the decision would impair economic growth in the near term and reiterated its view that Brexit remains a "significant" risk for the country.

Britain's Office for National Statistics published its 'flash' estimate for third quarter GDP Thursday - the first full three month period since the Brexit vote - in a report that showed the economy had expanded by a better-than-expected 0.5%. 

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Benchmark U.K. government bonds, however, extended gains Friday, pushing yields on both 10-year and 30-year Gilts to post Brexit vote highs of 1.3% and 1.95% respectively as investors trimmed bets on further interest rates cuts from the Bank of England. 

S&P's decision on June 27 stripped the country of its final triple-A rating, following cuts from both Moody's Investors Service and Fitch Ratings. Each of the three major agencies holds negative outlook on their ratings assessment.