It came as Paddy Ashdown, the Liberal Democrat leader, begins preparations to convince his party that its official stance of "equidistance" between the two major parties should be scrapped.
Mr Ashdown is understood to have privately decided some time ago that the position of equidistance is no longer tenable, and that the Liberal Democrats must spell that out well in advance of the next general election.
In an interview with New Statesman and Society, Mr Blair said, when asked about talking to the Liberal Democrats: "There are no proposals for anything institutionalised, but there are clear areas of overlap and agreement, for example in relation to the constitution. I don't see anything wrong with that. I don't take a tribal attitude to left-of-centre politics."
In a passage reflecting Mr Ashdown's own views, Mr Blair continued: "The problem for the Liberal Democrats is that the position of equidistance is not seriously tenable. It makes life difficult for those of us who recognise that there should be a proper dialogue of ideas."
The remarks will boost Mr Ashdown and a number of his senior colleagues who, while valuing their party's identity and independence, are unwilling to prolong the pretence that the Liberal Democrats' relationship with Mr Blair's "new" Labour Party and that with the current Government can seriously be portrayed as identical.
Mr Ashdown has campaigned for the "pluralist" approach to politics. Mr Blair said yesterday that involvement of Labour backbenchers in plans for a parliamentary Lib-Lab group were "sensible".
Asked about the prospect of co-operation with the Liberal Democrats in government, he said: "The most important thing is that we have a government that doesn't just say `we're the masters now, things have changed', but is deliberately trying to change the politics of the country - and that requires working to achieve the broadest possible basis of consent."
No date has yet been set for Mr Ashdown to ask his party to endorse the end of equidistance - although some senior figures are pressing for it to be done at this year's party conference or risk defections to "new" Labour.
They insist that Mr Blair's modernisation of Labour presents not a threat but an opportunity. In contrast to past elections, the traditional Tory device of "vote Liberal, get Labour" could backfire significantly at the next one, they argue.Reuse content