Lord Robert Maclennan of Rogart, former leader of the Social Democrat party, who also served as joint interim leader of the Liberal Democrats, has died.

The peer led the SDP in the late 80s as it carried out negotiations to merge with the Liberal party. Lord Maclennan then became joint interim leader of the merged party. He served as an MP from 1966 to 2001.

Bill Rogers, Roy Jenkins, David Owen and Robert Maclennan at a conference to launch the party’s draft constitution. Photograph: PA

Ed Davey, acting leader of the Lib Dems, said: “It is with great sadness that we learn our friend and colleague Bob Maclennan has died.

“Bob was the kind of politician we all strive to be. Considerate, honest and hardworking with an uncanny ability to reach out across the political spectrum to find common ground.

“He was also a great servant, over many decades, to his Highland constituents. A passionate advocate of devolution, he campaigned tirelessly for the creation of the Scottish parliament and wider constitutional reform.

“As Liberal Democrats, we also pay him a huge debt of gratitude. It was his determined leadership and bravery that proved critical in the formation of the movement we know today.

Lord Robert Maclennan retired at the 2001 general election. Photograph: William Conran/PA

“I personally owe a huge debt to Bob. He advised me through my own career and was a real source of strength and encouragement. His love of the arts and his commitment to a fairer society shone through so many of our conversations.

“Bob made our politics and our country better. He will be sadly missed and my thoughts and prayers go out to his family and friends.”

Dick Newby, leader of the Lib Dems in the House of Lords, said: “Bob Maclennan was passionate about Europe, constitutional reform and social justice.

“He saw them all as interconnected and pursued them with energy and determination throughout his political career. I worked with him for almost 40 years and will miss him greatly.”

Maclennan, who was a Labour MP before joining the SDP, was parliamentary under-secretary at the Department of Prices and Consumer Protection in the late 1970s.