THE Heinz Gallery of the Royal Institute of British Architects was a lovely old place. First you’d have to know it existed. It didn’t exactly advertise itself. Then you’d have to find it, reticent behind a dimly signed, well-to-do townhouse on Portman Square in Marylebone. Inside were splendidly obscure exhibitions of reverentially lit architectural drawings themed on, say, English ecclesiastical architecture, 1947-60.

The lucky might, on occasion, be allowed into the crepuscular inner sanctum, where curators, dapper in tweed, knee-deep in sketches by Inigo Jones, would spend their days archiving or trotting out to pick up a priceless Palladio sketch someone had found in their chicken shed. They held lovely lunches and stopped for tea at three. It was like an exclusive club, gorgeous while it lasted, but — in this age of interactive museum experiences and access for all — doomed.

All history now. The loveable tweedy eccentric has been replaced by a whizzy new millennial one. Britain’s first permanent architecture gallery opens on Thursday at the V&A. We few pilgrims to the late Heinz will be agog at its glitzy interactive touch screens, cool grey Corian surfaces, Perspex cases and catwalk spotlights. Its glam design by Gareth Hoskins Architects turns the Heinz from curio shop to fancy Bond Street boutique.

Britain has lacked a permanent museum since the V&A — which placed architecture, queen of the arts, at its heart when it opened — drifted away from the subject in the early 20th century. The V&A still has great collections, but they are rarely displayed, while RIBA’s own collections are among the best in the world, the bulk amassed by the great curator John Harris. Magnificent as it was, Harris’s collection became an embarrassing problem in the 1990s for RIBA, which lacked the funds, space and, occasionally it seemed, the will to display it outside the single room of the Heinz.

For decades there’s been talk about establishing a proper national architecture centre, but, despite initiatives and good intentions, it has never taken off. There have been isolated moments of hope: a network exists of energetic local centres such as Cube (Centre for the Understanding of the Built Environment) in Manchester; Sir John Soane’s Museum with its often curatorially adventurous shows; the annual Architecture Week; Glasgow 1999 City of Architecture and Design. But no momentum.

Large institutions such as the Hayward host the odd architecture show, though it’s been a while since anything’s rivalled the Royal Academy’s Living Bridges in 1996. Few curators seem trained to cope with the Problem with Architecture Exhibitions, ie the absence of the subject itself, so that exhibitions must be pinned around fragments and representations.

The best architectural exhibition is out on the streets, which is why London Open House, Heritage Open Days and the Serpentine Gallery’s summer pavilion draw hundreds of thousands each year.

The sheer brilliance of the once hidden RIBA and V&A collections, though, is enough to overcome these difficulties. They shine against the demurely glamorous backdrop of Hoskins’s gallery: fragments — a capital from the Pantheon, a window from a Walter Gropius factory — priceless drawings such as Palladio’s Villa Pisani, and jewel-like models both familiar (the Lloyds Building) and eccentric (Buckminster Fuller and Robert Matthews ’s Tensegrity structure made from Meccano and string on the kitchen table one evening) are guaranteed to bring out the archi-nerd in everyone.

Bonded at last by the National Lottery’s knight in shining armour, and given the surroundings and resources they deserve, the two collections create a centre whose breadth and depth no other institution can match.

The Heinz’s eccentricity has gone, alas. Anoraks will have to content themselves with seeing such jewels beautifully displayed. The curating here is resolutely populist, from the opening model of an interwar commuter semi, made by a builder called Mr Theobold for his daughter, through displays on how architecture is made, explaining such things as plan, section and elevation.

The subtext reveals how making architecture has changed through the ages — from Palladio’s ink drawings to Hadid’s fluid computer flythroughs for the PlayStation age — yet not changed: architects still draw back-of-the-envelope eureka-moment sketches. Huge new stores and study rooms in the Henry Cole Wing allow the public to walk in off the street and demand to see obscure 18th-century scribbles.

From famine to feast. For the gallery heralds a moment of unprecedented activity in architectural curating. The V&A may have lost Daniel Libeskind’s Spiral but it is embarking on FuturePlan, a necessarily more realistic and long overdue brush-up of more hidden treasures. RIBA is getting its act together, appointing Charles Knevitt, the former Times critic turned fundraiser, as head of the cultural trust supporting its library and collections. The Design Museum under Alice Rawsthorn, despite recent controversies, has never looked better. The Architecture Foundation in London, after years of not quite building the capital a contemporary architecture centre, last week announced a stellar, left-field shortlist, including Zaha Hadid, Foreign Office Architects MVRDV and a smattering of straight-out-of-college youngsters, to build its new HQ behind Tate Modern. The Heinz may be dead. But at least architecture’s alive and well.

• The Architecture Gallery, Study Rooms and Archives open at the V&A on Thursday, (020-7942 2000), www.vam.ac.uk, architecture.com.