National promised before the last election that it wouldn't sell or partially sell any state assets during its first term in office, but it hasn't made any commitments beyond that.
Speaking at a post-budget function in Christchurch today Mr English told business leaders the Government would "get to grips" with its position on state asset sales in the next eight months, the Stuff website reported.
Answering questions from the audience, Mr English said Kiwibank had reached a size where it needed either a government guarantee or "an awful lot of capital".
He suggested there would be strong demand for shares in it.
"But we have made undertakings to the public and we certainly won't move anywhere without getting a mandate to do so," he said.
Progressive Party leader Jim Anderton, who founded Kiwibank when he was a minister in the previous government, said the bank was a huge success because it was publicly owned.
"National's threat to sell Kiwibank is economic vandalism," he said.
"National repeatedly promised not to sell Kiwibank...people worried about Australian banks buying Kiwibank will immediately be concerned."
