By the late 1960s, the National Front was "the principal electoral force on the extreme right in Britain", and in 1981 Fielding noted that the NF "dominated" Britain's "extreme Right". In 1998 Durham stated that the NF and BNP had been the most significant far-right British groups since the Second World War. By 1977, the NF was England's fourth largest political party in terms of electoral support, and in some areas had threatened to replace the Liberal Party as the third largest force in British politics. This success was something which—according to Thurlow—"testified to the significance" of the immigration issue in 1970s British politics. A 1980 study by Martin Harrop, Judith England, and Christopher T. Husbands noted that the NF did not attract the levels of support enjoyed by the Liberal Party in England, the Scottish National Party in Scotland, or Plaid Cymru in Wales.