45 candidates in the 1969 local elections and averaged a poll of 8%, although a few secured over 10%. The party focused on these latter seats in the 1970 local elections, fielding 10 candidates; almost all received under 5% of the vote. The party faced militant left-wing opposition, including the driving of a lorry into its Tulse Hill building in 1969, and to counter this the NF installed a spy in London's anti-fascist movement. Against Chesterton's wishes, NF activists carried out publicity stunts: in 1968 they marched onto a London Weekend Television show uninvited and in 1969 assaulted two Labour Party ministers. While Chesterton was holidaying in South Africa, a faction led by Gordon Brown—formerly of Tyndall's GBM—launched a leadership challenge against him. On realising that his support was weak, Chesterton resigned. He was succeeded by John O'Brien in February 1971. Frustrated that Tyndall maintained links with neo-Nazi groups like the Northern League, O'Brien and his supporters ultimately left the NF for the National Independence Party in June 1972. Tyndall's first leadership: 1972–1975 Tyndall became party chairman in July 1972, centralising the NF's activities at a new Croydon headquarters. According to Thurlow, under Tyndall the NF attempted to "convert racial populists" angry about immigration "into fascists". In his history of fascism, Roger Eatwell noted that with Tyndall as chair, "the NF tried hard to hide its neo-Nazism from public view, fearing it might damage popular support." Refocusing its appeal towards the white working class, in June 1974 it launched the NF Trade Unionists Association. Britain's leftists fought back by publicising the neo-Nazi past of senior NF members, including photographs of Tyndall wearing a Nazi uniform. The NF capitalised on fears surrounding the arrival of Ugandan Asian refugees in 1972, resulting in rapid growth of its membership. At the 1973 West Bromwich by-election it gained 16% of the vote, passing the 10% mark in a parliamentary election for the first time, something that brought greater media coverage. 54 candidates were fielded at the February 1974 general election, a number that guaranteed them a party political broadcast. It contested six times as many seats as in 1970, averaging a vote share of 3.2%, slightly less than in 1970. By the mid-1970s, the NF's membership had stagnated and in several areas declined; all of its 90 candidates for the October 1974 general election lost their deposits. In the 1975 local elections they fielded