19 March 1977
In a joint declaration the leaders of the United Party (UP), Sir de Villiers Graaff and the Democratic Party (DP), Theo Gerdener, expressed their agreement to form a new party on the basis of equal rights for all racial groups in South Africa. No actual unification was immediately announced following this declaration. During the same year, a group of UP members left the Party to form the Committee for a United Opposition, which then joined the Progressive Reformed Party (PRP) to form the Progressive Federal Party. It is not clear whether this was prompted by the declaration between the two organisations. On 5 October, 1977 Sir de Villiers Graaff announced his retirement from politics, having been leader of the opposition from 1956 until the dissolution of the UP on 28 June 1977.
References

O’Malley, P., ‘1977’, from Nelson Mandela Centre of Memory, [online], Available at www.nelsonmandela.org.za [Accessed: 14 February 2013]|SAHO, ‘Sir de Villiers Graaff announces his retirement from politics, having been leader of the opposition from 1956 until the dissolution’, from South African History Online, [online], Available at www.sahistory.org.za [Accessed: 14 February 2013]|SAHO, ‘Democratic Alliance (DA)’, from South African History Online, [online], Available at www.sahistory.org.za [Accessed: 14 February 2013]