By Sophie Tanno, CNN London (CNN) — UK Prime Minister Keir Starmer has hit out at people “trying to interfere in our democracy” after US Vice President JD Vance waded into a national controversy by blaming “mass migration” for the recent murder of a student. The killing of Henry Nowak, an 18-year-old White student, sparked a national outcry after it emerged that police officers had handcuffed him as he lay dying from stab wounds inflicted by Vic…