Traffic growth is slowing, partly on uncertainty about a Brexit deal, agency says. : Ratings agency Standard & Poor’s has warned that Brexit could harm UK airport businesses, potentially threatening credit ratings if leaving the EU proves severe. In an analysis paper, Countdown to Brexit: The Growing Risks For UK Airports, S&P Global Ratings said although the country’s airports had enjoyed a grace period after the UK’s EU membership referendum two years ago, the repercussions of the split process were now starting to have an effect.