Iran is facing a return of UN sanctions - what happens now?

Britain, France and Germany have launched a 30-day process to reimpose U.N. sanctions on Iran over its nuclear program, according to a letter sent by the three nations to the U.N. Security Council seen by Reuters.
They accuse Iran of failing to abide by a 2015 deal with world powers that aimed to prevent it from developing a nuclear weapon. So what's next? Lucy Fielder has more.