The prime minister has repeated his view that independence would be economically disastrous for Scotland.
Mr Blair thinks Scotland would suffer under independence
Tony Blair was asked about comments from the head of the Roman Catholic Church in Scotland in which he backed independence north of the border.
Cardinal Keith O'Brien said he would be "happy" if people in Scotland wanted separation and claimed independence would come "before too long".
Mr Blair was speaking at his monthly Downing Street news conference.
He was asked if it was appropriate that a churchman should be making such comments a few months before the Holyrood elections.
In a newspaper interview, Cardinal O'Brien cited the success of smaller independent nations such as Ireland and Denmark to support his views.