The former leader's parting shot was intended to ensure the Liberal Democrats stay on the course he plotted for closer links with the Blair government, resisting the calls by some activists this week for a break with Labour.
Although Mr Kennedy said he supported Mr Ashdown's remarks, it will have sounded alarm bells in his camp that the former leader may be tempted to follow Lady Thatcher's example of "backseat driving".
With his voice breaking at times with emotion, Jane Ashdown, the former Liberal Democrat leader's wife, was moved to tears and left weeping during the standing ovation as Mr Ashdown and Mr Kennedy gave a "thumbs up" show of unity.
Mr Ashdown's former aides were also close to tears when he paid tribute to the party. "You have given me quite simply the pride and purpose of my life. To have had the privilege to lead you has been the greatest thing I have ever done or will ever do," he said.
Mr Ashdown, who was only denied a seat in the Blair cabinet by Labour's unexpected 1997 landslide, said it had been a great party to lead, but never easy. "You have been uncompromising at times when I wanted you to bend a little. Uncomfortable at others when I could have done with an easier ride. You have been unbelievably stubborn when I tried to take you in a direction you didn't want to go. And unbelievably curmudgeonly at times when I thought I was delivering success."
Recalling the personal crisis in his leadership when his extra marital affair was exposed, Mr Ashdown added: "You have been recklessly generous in forgiving my faults."
One Ashdown ally said: "He is saying things only Paddy could say to the party."
Mr Ashdown warned the Liberal Democrats against being too "staid and conservative" and to avoid old Labour tendencies to defend the producers against the consumers, parents and patients.
Urging his party to engage in fresh thinking, Mr Ashdown said: "In some areas we are, I fear, running the risk of becoming lazy and complacent in our thinking. If we Liberal Democrats will not think afresh, then we risk falling into the easy trap of leftist oppositional politics. And that would mean making ourselves irrelevant again for a generation."
Mr Ashdown took over from David Steele in 1988 when the Liberals' morale was low after repeated election disappointments. The new leadership is keen to avoid the mistakes highlighted by Mr Ashdown and moves were being made to block Simon Hughes - a leading critic of closer ties with Labour - from winning the deputy leadership. He will be given Alan Beith's portfolio as home affairs spokesman, but efforts are being made to persuade Mr Beith to stay on as deputy leader to keep Mr Hughes out of the post.