Just before 6am on the morning of July 5 1967, a bill decriminalising homosexuality ended its slow, tortuous progress through the House of Commons.

Two weeks later, the Sexual Offences Act received its Royal Assent. It was the beginning of the end of the persecution of gay men in Britain and the foundation upon which later measures to bar discrimination, introduce civil partnerships and, finally, legalise same-sex marriage would eventually be built.

The bill’s author was Leo Abse, a colourful and controversial Jewish Labour MP who represented the South Wales mining constituency of Pontypool. Abse entered the House of Commons in 1958, one year after the publication of the Wolfenden Report had recommended that gay sex between consenting adults should no longer be illegal. Parliament, however, had no appetite for such a move and overwhelmingly rejected the proposal. Over the next decade, a series of unsuccessful attempts — most notably by Lord Arran and the gay Conservative MP Humphry Berkeley — were made to act on Wolfenden’s proposals.

When Berkeley lost his seat in the 1966 general election, Abse took up the fight. His first wife, Abse later suggested, was an artist and had many gay friends, but it was his experiences as a Cardiff solicitor before he became an MP which most affected him. He saw first hand the manner in which gay men were subjected to blackmail as a result of the law, when he came to the aid of a vicar who, under the threat of exposure, was being forced to pay the legal fees of various local criminals. Introducing his bill in July 1966, Abse thus denounced the existing law as “an invitation to hoodlums”.

Thanks to the support of the Home Secretary, Roy Jenkins, Abse was able to secure government time for his Private Member’s Bill. Despite that, and Labour’s huge majority, success was by no means guaranteed. But Abse proved a skilful parliamentary pilot: calling in favours from mining MPs who opposed the bill to ask them to stay away from votes, while ensuring that during the crucial report stage he always had 100 MPs in the chamber to cut off debate and prevent filibustering.

More controversially, Abse was also forced to accept what he later admitted was an “absurdly high” and unequal age of consent of 21. The act also excluded the armed forces and merchant seamen, as well as Scotland, Northern Ireland and the Channel Islands. Moreover, prosecutions for gay sex actually went up in the years after the act was passed. Abse later resented what he viewed as the gay community’s lack of gratitude for his efforts. In truth, Abse was right that his legislation secured all that was achievable at the time, while gay men justifiably chaffed at the inequalities to which they were subjected until the age of consent was finally equalised in 2001.

The 1967 act was not Abse’s only contribution towards making Britain a more liberal and civilised country. He was also at the forefront of the battles to abolish the death penalty, to make divorce easier and increase access to family planning. Abse believed that being Jewish contributed to his liberal outlook: “The confident sense of identity which comes from belonging to an older culture meant that you were not intimidated by the prevailing ambience.” At the same time, however, Abse was no libertine: he called for the rock star Alice Cooper to be banned from Britain, denouncing his act as “the culture of the concentration camp”. He was also a fierce opponent of abortion and fought to restrict liberalising measures passed in the 1960s.

As Chris Moncrieff, the Press Association’s long-standing Westminster editor, suggested on Abse’s death in 2008, with the MP’s “fluent and sparkling Welsh waffle” he knew how to capture the attention of the press.

Partly as a result, Abse “got more backbench socially reforming legislation on the statute book than any other individual MP in the 20th century.”

Or, as his friend, the former Prime Minister, James Callaghan, once told him: “You do much more good in terms of human happiness than 90 per cent of the work done in parliament on political issues.”