A key moment in Charles Brett’s life occurred in 1956 when, at the age of 27, he was invited to join the Northern Ireland committee of the National Trust. Innocently enquiring what books he should read to fit himself for the task, he was told there were none to be had - an assertion he later found to be “substantially true”. In that instant a resolve was formed in his mind to make good the deficiency himself, a resolve he carried out with the utmost thoroughness and virtuosity.

He wasted no time in getting to grips with the enterprise. People going about their business in Belfast’s city centre during the late 1950s might have wondered at the occupation of a tall, fair-haired young man with a notebook and pencil, and the attention he seemed to be bestowing on buildings which everyone else either took for granted or mildly disparaged, according to the fashion of the day. In this manner - noting, recording and appreciating - Brett’s great work as Northern Ireland’s premier architectural historian got under way.

He started, as he said himself, just in the nick of time, as the Victorian city with its Georgian underlay fell victim to the rage for redevelopment which overtook the whole of the United Kingdom in the 1960s; and then to the additional, local depredations of “politically motivated” arsonists and bombers, once “the Troubles” had taken root. Brett’s Buildings of Belfast, 1700-1914 when it was published by Weidenfeld & Nicolson in 1967, already contained much to lament, including Charles Lanyon’s School for the Deaf and Dumb, and the old Lunatic Asylum on the Falls Road, demolished, as Brett has it, in 1924, “by the lunatics of Belfast”.

There were three main strands to Charles Brett’s working life at the time. In 1950, he had joined the family firm of solicitors, L’Estrange and Brett, and his initial architectural scrutiny of Belfast was carried out during his lunch hour. He was also a keen member of the rocky Northern Ireland Labour Party, a would-be non-sectarian organisation caught between clashing factions, and destined to fade out of Northern Irish politics (though not before Brett had successfully chaired it for a number of years). By opting for socialism, rather than Unionism, he was subscribing to a view of the world not readily attributable to someone of his background (though among his ancestors, it’s true, were those of a similarly radical, anti-Unionist and even anti-clerical cast of mind).

He was born in 1928 in Holywood, Co Down, into a prominent legal family, and educated in England, at Rugby and Oxford, where he read History at New College, Oxford and was president of the Poetry Society. Then he spent a year in Paris, working as a broadcaster and journalist, and savouring the mildly bohemian pleasures of an unencumbered life abroad, before returning in 1950 to Ireland and all its provocations. Belfast, however - which he’d lumbered in his mind with a dismal backwaterish quality - he found bristling with an indigenous camaraderie and vitality. The worlds of the arts, and of trade unionism, gave him an outlet for all his gregarious, cultural and reformist tendencies.

As for the other kind of Unionism: as he says in his autobiography-cum-family-history, Long Shadows Cast Before (1978), in the face of Unionist smugness and self-satisfaction, and in view of the overbearing way the one-party state was run, there was nothing for it but to “stand outside and bung bricks at them: a duty that I performed to the best of my ability, and with relish, for the next 20 years”.

In that assertion, you catch the unmistakable tones of the independent-minded, witty and forthright campaigner for social justice and improvement in every area of life with which he came in contact: someone whose raison d’être was to uphold the values of reason, tolerance and civilisation, even if it meant (as a Labour activist) getting up on a cart, or climbing the Custom House steps (Belfast’s version of Speakers’ Corner) to cry up the necessity for change before a sometimes unenthralled audience. He did this in order not to shirk any aspect of the socialist agenda; but (he says) “I was more at home in a committee room than on the back of ... a lorry”.

Committee rooms come into the picture, in abundance. The year 1967 saw the founding of the Ulster Architectural Heritage Society, mostly at the instigation of Charles Brett - an organisation he was still serving, as President, at the time of his death. Chairman of Hearth Housing Association, of the Northern Ireland Housing Executive, Vice-Chairman of the Arts Council of Northern Ireland ... the list is formidable.

But the preservation of Ulster’s dwindling store of architectural treasures became Brett’s most cherished preoccupation, “the modest but delightful buildings with which previous generations have endowed the towns, villages and countryside”; and to the listing and evaluation of these he brought a poet’s eye and a solicitor’s discipline, allied to a kind of benign despotism which came into play whenever he considered that others were dragging their heels.

The last part of the 20th century was not, he noted wryly, an auspicious era for a Northern Irish conservationist. His own solicitors’ office, in one of Belfast’s few remaining Georgian terraces, suffered severe damage from a massive car-bomb which exploded nearby in 1972; and Brett himself was quickly among the teams of helpers, “filthy and often bleeding from scratches made by slivers of broken glass”, who worked day and night to clear up the mess. The office continued in use (it is still there, under different ownership), and during the subsequent bomb scares which plagued the city, causing mass evacuation of workplaces, Brett would carry his papers out to a traffic bollard near the City Hall - a makeshift solicitor’s desk.

With so much destruction taking place, the necessity to conserve what remained became even more urgent. Throughout the entire period of disruption, Charles Brett - who’d made himself into a connoisseur of the cobweb fanlight and the fluted wooden column - went on providing invaluable guides to the existing building heritage of the north. These culminated in the splendidly produced, vividly informative trio of volumes, Buildings of County Antrim (1996), Buildings of County Armagh (1999), and Buildings of North County Down (2002), in which scholarship and idiosyncrasy combine to make a sparkling effect.

Going his own way, with elegance and aplomb, Brett stood in his lifetime as an antidote to the madness, complacency and inertia which bedevilled his birthplace; and if his impatience with diehards and ditherers alike sometimes got people’s backs up, the vast and eclectic nature of his circle of friends is a testament to his kindness, generosity, originality and verve. He was a delight to know.