LONDON (Reuters) - The risk of lower economic growth in central and eastern Europe (CEE) has started to rise in the wake of Britain's vote to leave the European Union, credit rating firm Standard & Poor's said on Wednesday.

S&P has negative outlooks on three of its 17 CEE sovereign ratings -- for Poland, Croatia, and Montenegro -- with stable outlooks on the other 14.

"With the UK electorate having decided to leave the EU in a non-binding consultative referendum on June 23, S&P Global Ratings believes that downside risks to growth have started to rise across the (CEE) region," the firm said in a new report.

"More importantly, however, the Brexit decision may exacerbate political uncertainty in CEE on several fronts."

"The Visegrad countries (Poland, Czech Republic, Hungary, Slovakia) but also countries of South Eastern Europe like Bulgaria, Croatia, and Romania, may fear increased dominance by euro zone countries, notably France and Germany, further complicating policymaking within the EU," S&P said.

(Reporting by Marc Jones; Editing by Catherine Evans)