Charles Kennedy has said he is looking for his party to make "substantial" progress at the next election.

The Liberal Democrat leader said a "step forward" was needed for him to remain secure in his position as party leader.

"I think the party anticipates that I will go on as leader through the next parliament, which is what I intend to do," he told Sky News' Sunday with Adam Boulton programme.

"But I think the party is also ambitious and looking for a substantial step forward."

Kennedy also said the party should "keep its feet on the ground".

"I am not saying we will win the next election," he said. "Can we win it? Any party can win the election."

"What we mustn't do is limit our ambition, because I think there is a lot of people looking at us out there.

"If they think we lack ambition and at the same time lack credibility, we won't make progress.

"But if we have credibility and we are ambitious then we can make progress."