By Elizabeth Piper LONDON (Reuters) -Aid worker Nazanin Zaghari-Ratcliffe accused Britain and Iran on Monday of treating her like a political pawn, saying it should not have taken six years for London to secure her release from detention in Tehran. Appearing at a news conference in parliament in London, the 44-year-old said she would always be haunted by her time in prison but would slowly work to rebuild her life with her daughter, 7, and husband away from the spotlight. Zaghari-Ratcliffe, who holds both British and Iranian citizenship, returned to Britain last week from Iran, where she was h…