Margaret Hodge’s in-tray is throbbing this month. Lurking in the pile are three files for the new Culture Minister marked “Contentious!”, each offering her a politician’s perfect storm – whatever decision she makes, it’ll be wrong for someone. For nothing in the politics of architecture is more contentious than the listing of postwar buildings.

Each of the three London buildings up for listing – Robin Hood Gardens housing estate in Poplar, the Lloyd’s Building in the City and the US Embassy, Grosvenor Square – comes with its own particular brand of controversy. But beneath all three lies the same old question: why in the name of Dan Cruick-shank should we preserve this pile of old concrete/steel/actually-rather-nice-Portland-stone for posterity?

“Nothing seems to raise people’s passions quite like post-war architecture,” sighs Alan Powers, the chairman of the Twentieth Century Society, Britain’s chief watchdog for last century’s heritage. “I can’t see why.” He has been asked about this issue countless times since English Heritage began thinking about preserving postwar architecture more than a decade ago. Powers, though, is one of the converted. The Great British Public alas, so the stereotype goes, rarely finds as much beauty in an exquisitely poured, brutalist concrete wall as a Georgian façade. Hodge, ominously, included.

It’s always encouraging to see a new minister in charge of a portfolio who is informed, cautious and evenhanded with their subject matter. Encouraging, but rare. Hodge made the baffling decision to write in last month’s Grand Designs Magazine an article so batty it beggars belief. In it she rails against “concrete monstrosities”, proposing that “if a building is less than, say, 75 years old, we should be able to consider matters other than the architectural or historic value in deciding whether to list it.” Why? “Because they cannot take . . . the test of time, scrutiny in other areas needs to be tougher,” those other areas being the cost of altering the building, and its fitness for purpose. Quite why these areas apply to buildings under 75 years old more than to Georgian rectories is left opaque.

The criterion for listing a building is simple: is it, or is it not architecturally or historically significant? Period. Sadly, Hodge at the Department for Culture, Media and Sport has the last say on this, advised by English Heritage – presumably the “mysterious and unelected”, “hand-wringing, teeth-sucking” “grey suits” she attacks in the piece. Actually, these people, unlike the minister, are well-trained historians who know what they’re talking about, even if what they say may obstruct far more important business, such as, in the case of Robin Hood Gardens, “regeneration” or, for the US Embassy, the War on Terror. She even goes on to propose that for those who fail to convince her refined aesthetic judgment of their worth “a perfect digital image of the building . . . could be retained for ever.” Is she insane? She offers no rational explanation why 71-year-old buildings should be treated thus, but not 128-year-olds or 349-year-olds, other than that they haven’t stood “the test of time”.

Critical distance is, of course, vital. Styles usually drift from disdain to nostalgia. In the 1950s nobody thought twice about pulling down a Georgian terrace. A decade on we almost lost St Pancras Station. That’s why there’s already a 30-year delay in listing buildings, unless, as in the case of Lloyd’s, completed in 1986, the building is considered significant enough already to warrant special consideration.

Some – including English Heritage’s chief, Simon Thurley – have also argued in the past for special measures in dealing with postwar architecture. He says that its specific nature – its structural experimentation, the scale of its commonest building types, such as housing estates and hospitals, all buildings prone to continual change – means that the listing system introduced after the Second World War needs reforming. Alan Powers, though, is having none of it. “There is nothing inherently different about postwar buildings.” He has a point. There are massive, architecturally experimental complexes prone to continual change in every century – the Tower of London, anyone? “We should judge like with like,” he adds.

“In any case people have this peculiar assumption that listing equals preservation.” Even buildings in the highest grade, I, are not preserved in aspic. By grade II, which make up 92 per cent of our 370,000 listed buildings, the building can be heavily altered. “In the case of Robin Hood Gardens,” Powers adds, “I’d be in favour of quite a substantial transformation.”

It’s not as if there are no precursors for this. The developer Urban Splash is innovatively transforming both Park Hill, the massive (Grade II* listed) postwar estate (and Robin Hood’s cousin) that glowers over Sheffield’s city centre, and Gillespie Kidd & Coia’s long-ruined Cardross Seminary outside Glasgow (category A-listed – Scotland’s listing equivalent), both once considered lost causes. Last week Rem Koolhaas’s Office for Metropolitan Architecture was appointed to restore and redesign London’s Commonwealth Institute (Grade II*) – a bold, but perfect choice. The Grade I Festival Hall’s rebirth last year has left it in its best shape for years. Transforming postwar architecture isn’t rocket science: it takes the same qualities as transforming architecture from any period – intelligence, effort, a sympathetic owner, collaboration, not confrontation.

In 2006, Hodge’s predecessor, Tessa Jowell, tried to delist the Commonwealth Institute, its trustees having for years found it too taxing to discover a new use for the 1960s has-been. Yet in one year a developer, Chelsfield, has managed it. It’s easy to treat postwar architecture with such scorn. It’s a convenient scapegoat, easily got rid of. Who’ll miss a carbuncle, eh?

Plenty. And our numbers are growing. “We have a very market-driven landscape,” says Powers. “Listing is the best, sometimes the only way to put the brakes on. It gives you a moment to pause and think before you lose something forever, and it does not – not – mean no change at all.” Still, soon, perhaps, Hodge will be troubled no more by a subject about which she clearly has little understanding. The Government’s Heritage Protection White Paper proposes devolving responsibility for listing to English Heritage. Not a moment too soon.

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