By Kelly-Ann Mills One of the countries top private schools which was once attended by Princess Kate is at the centre of a sexual assault investigation with a former teacher accused. Marlborough College, which the Princess of Wales is keen for her eldest son Prince George to attend, is taking the claims from the 1980s “extremely seriously”. Kate herself attended the £47,000-a-year school between 1996 to 2000. Police said a man in his 80s had been arrested on suspicion of a “non-recent sexual assault” at the school after a report from a member of the public. A Marlborough College spokeswoman sa…