LORD Goodhart, founding member of the Social Democratic Party and stalwart of the Liberal Democrats, has died aged 83.

William Goodhart QC was a retired peer and the co-author of the Lib Dem constitution and a human rights lawyer.

After founding the SDP he played a key part in the party's merger with the Liberals to form the Lib Dems in 1988.

Four years later he missed out on becoming MP for Oxford West and Abingdon by 4,000 votes but his team's campaigning paved the way for his successor Evan Harris to win the seat in 1997.

He was knighted in 1989 and made a Life Peer - Baron Goodhart of Youlbury - in 1997.

In the House of Lords he was the Lib Dem's shadow Lord Chancellor before being appointed Chair of the Delegated Powers Committee.

William Goodhart was born in Oxford on January 18, 1933, the son of American-born lawyer and jurist Arthur Lehman Goodhart, the first American to be the Master of an Oxford college - University College.

He was educated at Eton college alongside his younger brother Charles, an economist who would later become a member of the Bank of England's Monetary Policy Committee.

His elder brother Sir Philip Goodhart was a Conservative MP and Under-Secretary for Northern Ireland during part of Thatcher's premiership.

After finishing school, William undertook National Service for two years before graduating with a law degree from Trinity College, Cambridge in 1956.

He won a fellowship to study law at Harvard University and qualified as a barrister in 1959, later being appointed Queen's Counsel in 1979.

He married Celia Herbert in 1966 and the couple settled in Boar's Hill, just outside Oxford.

They had three children, two daughters Frances and Laura, and a son Benjie.

Following Roy Jenkins' Dimbleby Lecture in 1972 outlining the weaknesses in the British political system, William was inspired and joined the Council for Social Democracy and founded the SDP.

He chaired the SDP conference committee - and then the Lib Dem conference committee after the merger - for almost ten years.

He also unsuccessful ran in the Kensington by-election in 1988.

William was the parliamentary candidate for Oxford West and Abingdon in 1992, narrowly losing to Conservative candidate John Patten.

He died of Alzheimer's on January 10 and is survived by his wife Celia, his children Frances, Laura and Benjie, and three grandchildren.