Fitt, then Northern Ireland's only Catholic MP at Westminster, had taken pride of place at the front of the protest. Never a man to downplay a drama, he afterwards treasured his bloodied Marks & Spencer shirt and used the incident to focus the eyes of the world on the injustices suffered by Catholics in the north of Ireland since partition in 1921. Scenes of British MPs being charged by police made dramatic television.
Fitt, who had been elected to Westminster in 1966 as the Republican Labour member for West Belfast, had been working to draw the attention of fellow MPs in London to the situation in Northern Ireland, and had persuaded three Labour MPs to join the civil rights march, along with several journalists, notably Mary Holland, of the Observer.
The Northern Ireland civil rights movement was already attracting attention, but it was Fitt's determined campaigning that ensured that prime minister Harold Wilson took the problem seriously. Wilson later said that it was footage of the violence on streets regarded as British, and the concerns of his own Liverpool Irish constituents, that forced him to focus on the protesters. The home secretary, then James Callaghan, was duly dispatched to Derry.
Fitt's strengths were his gregarious ability to talk, drink and empathise across any divide, and his lack of caution when he felt an injustice threatened. It was that lack that gave him the courage, in the turbulent 1960s, to put his family and his life at risk to better the lot of Northern Ireland Catholics. For all his clubability, he was both a maverick and a loner. But his crucial role was that, when the civil rights movement needed it, he had the courage to kick off the brakes and set change rolling.
In his final years, Fitt became something of a hate figure to many who had marched alongside him in Derry, because he became increasingly opposed to the involvement of Dublin in Northern Ireland issues, and to the acceptance of Sinn Féin into mainstream politics. He always saw Northern Ireland's future as linked to London, not quite as the Unionists wanted it, but with London, not Dublin, as the main axis.
In 2002, Gerry spoke and voted in the House of Lords against the dismantling of the Royal Ulster Constabulary -which had baton-charged him in 1968 - and its replacement, in a bid to win Catholic support, with the Police Service of Northern Ireland. He was seen by critics at home as out of touch; dangerously so because his views were respected by politicians in London.
His irrepressible tongue caused difficulties with other politicians. When I was a Guardian reporter in Belfast, it was as well to allow plenty of time when phoning him, for he had a fund of stories. "Wait up, wee girl, while I shut the door. I don't want Anne (his wife) to hear me tell you this one ...", he would say while still MP for West Belfast. After three or four jokes - most barbed about fellow politicians, particularly those theoretically closest to him - he would get round to current events.
He always had something apposite to say. Politics was his lifeblood, shaped by his birthplace: tough working class Catholic Belfast. He was educated there by the Christian Brothers and left school to work in a barber's shop. At 15 he joined the merchant navy, serving in it from 1941 to 1953. During the second world war he sailed on Russian convoys.
In the merchant navy he was active in the seamen's union and taught himself law and politics. He claimed that watching Protestant politicians campaigning in Belfast as a child made him want to go on the stump, and when he left the sea, he ran for Belfast city council, and then the Stormont parliament, as the Republican Labour candidate for the docks area of the city.
In 1970, Gerry was one of a disparate group of leaders of the Catholic community, including John Hume, Austin Currie, Paddy Devlin and one sole Protestant, Ivan Cooper who formed the Social Democratic and Labour party. His Westminster seat ensured him the leadership, but his relationships with several of the others, notably Hume, his deputy, and Devlin, a fellow Belfast socialist, were turbulent. He regarded Hume as too nationalist; indeed Hume, who saw himself as a social democrat, had tried to keep the word "Labour" out of the party's title. Gerry and Devlin, from similar backgrounds and with similarly explosive temperaments, once had to be dragged out of a fist fight behind the speaker's chair at Stormont. However, they all managed to work effectively together in the negotiations that led to the December 1973 Sunningdale agreement, brokered by the Conservative prime minister, Ted Heath, and in the shortlived power-sharing executive that summer.
Gerry served as deputy to the chief executive, Brian Faulkner, the Unionist leader who had been the last Stormont prime minister before it was suspended by the British in 1972. Gerry blamed the government for allowing the collapse of the executive. It had been, he said, the best chance of a reasonable political settlement. He blamed Hume, too, for insisting during the Sunningdale talks on a Council of Ireland with a Dublin dimension and criticised the 1998 Good Friday agreement, negotiated by Hume, for the same reason.
He believed that Unionist hostility would have been much less had Dublin been kept at arms' length. As far as he was concerned, Hume prevented him from achieving his political end. The lack of warmth was mutual.
At Westminster he maintained links with the Labour party and voted usually with the Wilson government, and from 1976 with the Callaghan government. But he abstained on the vital vote of confidence that brought down Callaghan in 1979 because of his disillusionment with the then Northern Ireland secretary, Roy Mason.
Their bad relationship, dated from Mason's refusal as secretary of state for defence, to send in troops against loyalist strikers in 1974, a direct cause of the collapse of the power-sharing executive. In the Lords' bar, when both were well into their 70s, Gerry would mutter "that wee fucker" when Lord Mason came in.
In 1979, after bitter rows with Hume over Irish government involvement in fresh constitutional talks, he resigned the SDLP leadership. He lost his Westminster seat in 1983 to the Sinn Féin leader, Gerry Adams. The SDLP was in crisis over its ambivalence to the deaths in 1981 of 10 IRA hunger strikers in the Maze prison, including Bobby Sands, who was elected as Westminster MP for Fermanagh and South Tyrone, while on his deathbed. The SDLP did not field a candidate against Sands, conscious of how much anger there was in the Catholic community about the Maze deaths. Gerry had spoken out against the hunger strike, which was a protest for political status for paramilitary prisoners, orchestrated by Adams and Sinn Féin. He blamed the SDLP for allowing the rise in Adams's popularity that let him capture the West Belfast constituency.
Gerry suffered a second heavy blow in 1983 when the family home in the Antrim Road was burnt down by the IRA. The house, known as Fortress Fitt after security grills and an entry phone system had been installed, was in an area of north Belfast patchworked with protestant and Catholic enclaves, and notorious for the highest number of sectarian attacks in Northern Ireland.
The security measures had been put in place after IRA sympathisers broke in, one night in 1976, as the Fitts were getting ready for bed. They were fended off by Gerry, in his underwear and waving a Browning automatic, issued officially to him during the period of the power sharing executive. But no amount of protection could stop the Fitt home being a target to Loyalists and the IRA.
Gerry had some sympathy, though, with young rioters. "Anyone born after 1969 knows nothing but throwing stones at police and robbing post offices and knee-capping people," he said at the time of the 1994 ceasefire. But he remained hostile to the Provisional IRA, joining forces in the Lords in 1999 with an old opponent, former Unionist party leader, James (now Lord) Molyneaux (to oppose immunity given under the Good Friday agreement for IRA killers, after the graves of vanished victims of IRA violence were revealed.
The one consolation which an otherwise bleak 1983 brought was the seat in the Lords. This made Gerry's retirement from Belfast politics a joy, but it did nothing to tone him down. He remained the same character who, during the Ulster Workers strike in 1977, would step on to a London-Belfast flight laden with loaves of sliced bread to take home to strikebound neighbours - and fortify himself with miniature bottles of gin during the journey.
It was usual to see him at SDLP party conferences in the 1970s holding a handful of tablets for stomach problems and a glass of gin, joking that one or other would finish him off
In the Lords he became a fixture: the centre of a disparate group of fellow peers, from right and left in Britain and Northern Ireland. His mind retained its sharpness, his anecdotes their bite.
It is impossible to assess how the SDLP would have fared if Gerry and Hume had continued to work in it. But Gerry's inner-city socialism sat better with Labour in London, while Hume worked better with Dublin and politicians and diplomats on the continent. Its failure to progress further pushed Gerry, who is best judged on his 1968 performances rather than his 1983 ones, into an early departure from Belfast politics.
He returned only rarely to Northern Ireland for 10 years after 1983 - then bought a weekend cottage in the Glens of Antrim. The Fitt's marriage retained its romance. Each year, on the anniversary of their first date, Gerry would buy stockings and chocolates and repeat his journey to see the woman who would become his wife. Anne, also Belfast-born, had been working in a hotel in Piccadilly in the heart of London. He had travelled most of the way by bus - but had taken a taxi the last yards to make a grand entrance. Anne died in 1996 from a hospital super-virus contracted during routine treatment.
Five of Gerry's daughters - he always referred to them as "the Miss Fitts" - survive him.
· Gerard "Gerry" Fitt (Baron Fitt of Bell's Hill in the county of Down), politician, born April 9 1926; died August 26 2005
