The New National Party, having lost its Eastern Cape leader Wilhelm le Roux to the Democratic Alliance on Monday, suffered a further blow on Tuesday with the defection of Le Roux's deputy Tyrone Liberty to the United Democratic Movement.
Liberty is a member of the Eastern Cape provincial legislature.
In a statement on Tuesday, UDM leader Bantu Holomisa said Liberty "brings with him the executive and branch members of his area".
"He has made a wise decision, recognising that the NNP has served its purpose on the South African political landscape."
While the NNP "is in terminal decline, the UDM is growing strongly and receiving scores of card-carrying members from other parties, especially the ANC".
This represented a shift in voter support on the ground, Holomisa said. - Sapa