Following Northern Rhodesia's independence as Zambia in October 1964—Nyasaland had been independent Malawi since July—Southern Rhodesia began referring to itself simply as Rhodesia, but Whitehall rejected this change. Perceiving Smith to be on the verge of a unilateral declaration of independence (UDI), Wilson issued a statement in October 1964 warning of dire economic and political consequences, and wrote to Smith demanding "a categorical assurance forthwith" that no UDI would be attempted. Smith ignored this, expressing confusion as to what he had done to provoke it. The UK and Rhodesian governments exchanged often confrontational correspondence over the next year or so, each accusing the other of being unreasonable and intransigent. Little progress was made when two Prime Ministers met in person in January 1965, when Smith travelled to London for Sir Winston Churchill's funeral. The RF called a fresh election for May 1965 and, campaigning on an election promise of independence, won all 50 "A"-roll seats (elected mostly by whites). Wilson's ministers deliberately stonewalled Smith during mid-1965, hoping to eventually break him down, but this only caused the Rhodesian hierarchy to feel yet more alienated. From June, a peripheral dispute concerned Rhodesia's unilateral and ultimately successful attempt to open an independent mission in Lisbon; Portugal's acceptance of this in September 1965 prompted British outrage and Rhodesian delight.