UPDATE 1 — UK PM Burnham and Irish PM Martin reaffirm commitment to Good Friday Agreement
(Adds quote, background in paragraphs 2, 4-5) LONDON, Sept 18 (Reuters) — Britain's Prime Minister Andy Burnham and Irish leader Micheal Martin on Friday reaffirmed their commitment to upholding the Good Friday Agreement, Downing Street said in a statement issued after the two leaders met in Manchester. The 1998 Good F