The political world has paid tribute to Paddy Ashdown – the irrepressible former Liberal Democrat leader and ex-marine – who died aged 77 just two months after revealing that he was being treated for bladder cancer.

Lord Ashdown, who built the Lib Dems into a formidable third party at Westminster and a highly effective force in local government during his 11 years as leader between 1988 and 1999, died on Saturday evening, a party spokesman said.

After he stepped down from the helm of his party – having led it to its best general election result in more than 70 years in 1997 (when the number of Lib Dem MPs rose from 18 to 46) – he remained hugely active and in the forefront of public life, combining his political interests with writing.

Paddy Ashdown: a political life in pictures Read more

Having left the House of Commons in 2001, Ashdown received a peerage and served for four years as the United Nations’ high representative in Bosnia-Herzegovina.

Despite commanding great respect for his many areas of expertise, particularly in foreign affairs, he never managed fully to shake off the “Paddy Pantsdown” moniker planted on him by a famous front page of the Sun newspaper. It followed the disclosure of a five-month-long affair with Patricia Howard, his former secretary.

An ardent pro-European, Ashdown styled himself as the “Action Man of politics” at the head of a party whose energetic and highly focused campaigning in byelections and in local politics was the reason for much of its success. He disliked being confined to Westminster and preferred to project himself as a leader in the thick of things, jumping out of helicopters and making regular trips to the frontline of the Bosnia conflict, jacket slung over his shoulder.

Sir Nick Clegg, who led the party from 2007 to 2015, said that Ashdown was “the most heartfelt person I have known” and “the reason I entered politics. He was the reason I became a liberal. And he became a lifelong mentor, friend and guide.”

Sir Vince Cable, the Lib Dems’ current leader, said it was “a hugely sad day” for the party and everyone else across politics “who had immense affection and respect for Paddy”.

He said: “Paddy was famous for his politics, but his talents extended well beyond that arena. He was an accomplished author, and had spent many years serving the country before he got near the Commons. Few people know how hard he fought to get into politics following his service in the marines and diplomatic service.”

After the 1997 election, in which Labour secured a landslide triumph, Ashdown and some of his colleagues were invited to join a cabinet sub-committee. Some saw this as the start of a coalition between the two parties, and Ashdown even spoke of the possibility.

But the outcry that followed this “feeler” caused the then-Liberal Democrat leader to intensify his attacks on Labour in the belief that people would assume he had dropped the idea. And although Ashdown always insisted that he was in politics to “do things, not to be things”, there was no doubt that he had longings towards a cabinet post in Tony Blair’s government.

Describing him as “excellent company, always fun to be around”, Blair said: “He was one of the most talented politicians never to hold high office, but as leader of the Liberal Democrats he nonetheless had a major impact on British political life.”

Ashdown disclosed in his diaries, published soon after he stood down as leader of the Lib Dems, that he and Blair had been involved in secret “coalition” talks before the 1997 general election.

In 2010, during talks that led to the formation of a coalition government, Ashdown had serious reservations about his party teaming up with David Cameron’s Conservatives, but eventually reconciled himself to the need, seeing it as in the national interest.

In his final years, Ashdown continued to be a regular contributor to agenda-setting political shows. However, in November this year, he revealed he had cancer.

“We must see about the outcome, which as always with things like this, is unpredictable,” he said. “I’ve fought a lot of battles in my life. This time I am lucky enough to have the magnificent help of our local hospital, and my friends and family, and that gives me great confidence.”