By mid-1981, Thatcher's leadership was in her "darkest hour"; her popularity plunged after the April Brixton riot and the July Toxteth riots. The Conservative leadership were also worried about the effects of the June SDP–Liberal Alliance. The SDP (Social Democratic Party) had been formed in March 1981 by the Gang of Four MPs who defected from the Labour Party; they were joined soon after by Christopher Brocklebank-Fowler, who defected from the Conservatives during a debate on Howe's budget. Polling showed Thatcher's approval rating was the lowest recorded for any prime minister and below that even of the unpopular Labour Party leader Michael Foot. The Conservative Research Department conducted polls in late summer that showed the popularity of the Alliance might render the Conservatives a minority party, achieving just 16% of the vote (compared to the SDP–Liberal 40%) which would be their worst election performance for 100 years. It was feared by the Conservative leadership that the party was close to splitting.