S&P 500, Nasdaq futures slump 5 percent as Britons vote to leave EU

The drastic drops in U.S. stock index futures prices suggest Wall Street will open with steep losses on Friday. British markets plunged, with sterling hitting a 31-year low in its biggest fall on record and UK stock futures pointing to a steep fall at the market open after Britons voted to leave the European Union. Asian markets also tumbled.