Protesters threw bottles, cans and smoke bombs at riot police in central London on Saturday in a demonstration against the re-election of Britain’s Conservative Prime Minister David Cameron. Scuffles broke out when the demonstrators, blaring hooters, banging pots and chanting obscenities, confronted lines of police outside the gate leading to the prime minister’s Downing Street residence. At one point a bicycle was hurled at police. Police arrested four people, and two officers suffered minor injuries, a Scotland Yard spokesman said. A Reuters photographer estimated that a couple of hundred people took part in the protest, including a group of about 25 black-clad youths with sunglasses and face masks. He said police briefly closed the central Whitehall avenue to traffic but later reopened it and surrounded the last remaining group of several dozen protesters.