(Reuters) -Britain's Spectris has accepted an improved takeover offer from U.S. private equity firm KKR, valuing the scientific instruments maker at about 4.7 billion pounds ($6.46 billion), including debt, the companies said on Wednesday.

Spectris said its board has decided to withdraw its recommendation of Advent's 4.4-billion-pound offer in favour of the higher bid from KKR.

($1 = 0.7281 pounds)