IT was Hugh MacDiarmid who, in a moment of divine inspiration, described Edinburgh as "a mad god's dream" from which "earth eyes Eternity".

Returning to the city, either by rail or road, I am often struck by its insistent beauty and wish, like a tourist, I was eyeing it afresh. There's the castle rising to the south and the Forth twinkling to the north. To live and work and play in such a place is a privilege which one dare not take for granted. Daily, it lifts the spirits and makes you feel that here at least we produced something with which a visitor from Florence (its twin city) or Athens might feel comfortable. As even Edwin Muir conceded, the first impression one has of Edinburgh is of "rocky splendour and pride". Crucial to this is the harmonious conjunction of old and new, of the asymmetric, organic chaos of the Old Town, with its spires and tenements and closes, and the precise, pleasing and dignified classicism of the New Town.

Of late, however, Edinburgh has begun to slip in my estimation. I will always love it but whether I will love it as much as I did I am beginning to doubt. Not so long ago, I was standing at the lights where Dundas Street meets Queen Street. Alongside me stood an elderly gent, who may just have come from lunch at his club. Next to him was a family from foreign parts, who asked the gent for directions, which he helpfully gave, then added, apropos nothing in particular: "Edinburgh used to be such a handsome city." I know what he meant. Everywhere one looks one begins to spy ugliness and unkemptness, unnecessary fuss and the intrusion of the alien.

At St Andrew Square, where I often catch a bus to the boondocks, and where in the heyday of the Enlightenment houses once stood, there is gap site the size of Torremolinos. Nearby stands the last Georgian block between the square and General Register House at the east end of Princes Street, which has been earmarked for demolition. Further to the east, in the lea of Calton Hill, is the old Royal High School which has been empty for as long as I care to remember. Once upon a time it was to have housed our reconvened parliament. When that idea proved unpalatable, it was to have become home to a Scottish National Gallery of Photography but that, too, was pushed into the long grass. Now, it seems, it is to become a hotel, though not before the integrity of the original masterpiece has been brutally impugned. Has no one ever thought of re-imagining it as a school?

The best view of the Royal High is from the Canongate cemetery, where lie the poet Robert Fergusson and the philosopher Adam Smith. A stone's throw from it is Caltongate, a humungous development that may yet rival the St James Centre for sheer inappropriateness. When finished it will include budget hotels, shops, office accommodation and a couple of hundred houses. That sounds, and looks, like one of those developments you might be able to forgive if it was on the outskirts of Nowwhereville but which, in the heart of Edinburgh, makes you want to weep.

One could go on; one must go on. In the Cowgate, where in 2002 fire destroyed venerable buildings directly beneath the South Bridge, there is another paean to bland, carbuncle-like modernism, with its straight, economical lines and ubiquitous acres of glass that allow you to look out of the horrible building you're unfortunately in to a pleasing cityscape fashioned 200 years ago. "I think the development looks all at peace with the rest of the street," said the managing director of the company that acquired the plot. He ought to make an urgent visit to Specsavers.

What's to be done in the face of such unapologetic insensitivity? It all reminds me of the 1960s when Edinburgh University was allowed by the planners to destroy George Square and erect buildings which are an affront to learning. There is, it would appear, an atrophic conspiracy of politicians and officials, developers, speculators and architects, to ignore Edinburgh's history and implant on it plooks which only wrecking balls can remove. Already several hundred people have attended a meeting in protest at what's proposed for the Royal High. But the problem goes much further than one building. Edinburgh's historic centre is under threat in all corners, hence the mooted request to Unesco to deprive it of its World Heritage Site status. One hopes that this will help concentrate minds. In the meantime, it may be that the bourgeois mob which in the early 1990s prevented the closure of the Scottish National Portrait Gallery will need to muster again. Tarry ye not.