The Dangers of Architectural Prophets

Not since the biblical era have we been prone to so many visions. To judge from the number of documents that land on my desk each week concerning politics, urban planning and architecture, this is truly an age of great visionaries. It is not simply major modern prophets such as George Bush and his fellow evangelical Tony Blair who have visions - of, among other things, a US-style liberal democracy in Iraq - but lesser divines further down the political ladder, too.

John Prescott, the deputy prime minister, has a vision of the Thames Gateway. In this vision, tens of thousands of people will lead the good life in mystic "sustainable communities". Nobody knows what these are, but then visionaries are rarely understood, and prophets much less honoured, in their own time and country.

This week's visions have included one of Thurrock, a part of "Thames Gateway", a new Jerusalem on the Essex floodplain, and another of the "People's Waterfront" at Liverpool. Many others have been sent from government departments, development agencies and quangos which, if they should be written every one, the world itself could not contain the books that should be written.

This last sentence is a slightly edited version of the final sentence of the Gospel of St John, the silver-penned evangelist who is, possibly, also St John the Divine, author of the Apocalypse, or Book of Revelation. St John's vision was of the coming of the kingdom of God, told in images and language that will continue to haunt future generations.

John describes a vision of "the holy city, new Jerusalem, coming down from God out of heaven, prepared as a bride adorned for her husband". Having the glory of God, this divine city lies four square and is built of such choice materials as jasper, sapphire, chalcedony and emerald. The street of the city is "pure gold, as it were transparent glass". From his vantage point on top of "a great and high mountain", to which he had been carried "in spirit", John sees no temple in the city of God, "for the Lord God Almighty and the Lamb are the temple of it". Specifying neither race nor class, he tells us that all saved people coming to the city "shall walk in the light of it".

Far from that of Thurrock and of the Waterfront at Liverpool, this is a true vision. Reality transcended. Poetically inspired. Spiritual glory. A city to aspire to, and pray for. Few of us in Britain at the time aspired to the long forgotten Millennium Experience or prayed for the Dome. Described unflaggingly by zealous politicians and their pious servants as "visionary", the Millennium Experience was no such thing.

No one had seen the Dome coming down from God out of heaven. Nor has anyone since had a true vision of Thurrock or the Liverpool Waterfront, although countless would-be St Johns and William Blakes believe that they have. Perhaps the streets of these new marvels will be paved with gold, and with the promise of vibrant, accessible 24-hour shopping malls, they may well eschew temples.

Visions are given to prophets and poets. To some great scientists too. In the mind's eye of those less blessed, they are cloudy things, best washed away with Optrex. We talk, promiscuously, of visions today, when we mean ideas, but more normally thoughts or suggestions in need of cobbling together to make practical sense. The Millennium Experience proved to be a shallow thing, a costly foible, with as much vision in its make-up as a coconut shy.

As for the planning of our cities and the construction of urgent new homes, visions are unhelpful. What we need is an earthly alliance of imagination, generosity, practical skill and common sense. Truly visionary cities are as rare as St John's. When they do exist, and Brasilia comes close, they are awkward things: wonderful to look at, hard to make work. If Brasilia works today, it is because of the shanty towns huddled alongside it, for "key workers" unable to afford life in the city's visionary centre.

Great civic leaders of less evangelical eras than ours did not speak of visions. They thought things through carefully, assessed risk, found money and built. The politicians and young architects of the former London County Council - who a century ago built fine council housing, admired worldwide, in the city centre for "key workers" - neither experienced nor described visions. Frank Pick, who made the former London Passenger Transport Board a work of art as well as the kind of fully integrated urban transport system we can only dream of today, had no vision, even though his mind was brilliant, illuminated with philosophy, literature, law, religion, and common sense.

In creating our new Jerusalems, we would do better to rely on common sense than indulge in a plethora of pseudo-religious visions. St John's city will always be there as the ultimate reward for our saintly politicians, visionary quangos, holyarchitects and divine developers. But neither on this earth, nor that "Waterfront" or "Gateway".

· Jonathan Glancey is the Guardian's architecture critic