Throughout the 1950s and 1960s, MK was in essence a political pressure group rather than a true political party, with members being able to join other political parties as well. It campaigned for the establishment of a Cornish University, a Cornish Industrial Board, and the repatriation of Heligoland Fresians whose land was used by the British government as a bombing range in the mid-1950s. It published numerous policy papers to support its positions. MK gained popularity in the 1960s, when it campaigned against 'overspill' housing developments in Cornwall to accommodate incomers from Greater London. In April 1967, Colin Murley was elected for MK onto Cornwall County Council for the seat of St Day and Lanner; he had stood on an anti-overspill platform. In 1968, the first edition of Cornish Nation was published; this is the party's magazine. However, by the 1970s the group developed into a more coherent and unified organisation. During this decade, MK began contesting Westminster parliamentary seats as well as local government ones. It held rallies in support of Cornwall's fishing industry and against regional unemployment and nuclear waste; in the 1980s, these rallies were aggravated by the policies of the incumbent Thatcher government. The party grew to become the leading champion for Cornish nationalism, superceding the Stannary Parliament in this respect. The party opposed the Common Market. MK contested the 1979 European Parliament election, winning 5.9% of the vote in the constituency of Cornwall and West Plymouth.
Question: How many centuries spanned when MK was in essence a political pressure group?
Answer: 2