the start of 1983 (it continued to be under 7% until 1990). The British economy benefitted in the first Thatcher ministry by tax income from North Sea oil coming on stream. The period of unpopularity of the Conservatives in the early 1980s coincided with a crisis in the Labour Party, which then formed the main opposition. The Social Democratic Party (SDP) was established in 1981 and consisted of more than twenty breakaway Labour MPs, who quickly formed the SDP-Liberal Alliance with the Liberal Party. By the turn of 1982, the SDP-Liberal Alliance was ahead of the Conservatives in the opinion polls, but victory in the Falklands War in June that year, along with the recovering British economy, saw the Conservatives returning quickly to the top of the opinion polls and winning the 1983 general election with a landslide majority, due to a split opposition vote. Thatcher now faced, arguably, her most serious rival yet after the 1983 general election, when Michael Foot resigned as Leader of the Labour Party and was succeeded by Neil Kinnock. With a new leader at the helm, Labour were clearly determined to defeat the Conservatives at the next election, and for virtually the entirety of Thatcher's second ministry, it was looking a very serious possibility, as the lead in the opinion polls constantly saw a change in leadership from the Conservatives to Labour, with the Alliance occasionally scraping into first place. By the time of the general election in June 1987, the economy was stronger, with lower inflation and falling unemployment and Thatcher secured her third successive electoral victory with a second, albeit reduced, landslide majority. The introduction of the Community Charge (known by its opponents as the poll tax) in 1989 is often cited as contributing to her political downfall. The summer of 1989 saw her fall behind Neil Kinnock's Labour in the opinion polls for the first time since 1986, and her party's fall in popularity continued into 1990. By the second half of that year, opinion polls were showing that Labour had a lead of up to 16 points over the Conservatives, and they faced a tough 18 months ahead of them if they were to prevent Kinnock's ambition to become Prime Minister from becoming a reality. At the same time, the economy was sliding into another recession. Internal party tensions led to a leadership challenge by the Conservative MP Michael Heseltine;