Stevie Carr

 and Andy Mills robbed the bank where Vernon Robey was depositing his money. They took Vernon's money, including the change from a pay telephone. When the police arrived, they took off. Stevie spilled the coins during his escape. The Sixth Doctor saw in the pile of coins the same one he had given to Si that morning. He then tripped Stevie and left him there for the police. (PROSE: Loose Change)