Fear not, the famous meat market is safe. For now, though for how long nobody can say for sure. But there is another part of Smithfield Market - a collection of agreeable Victorian buildings at the western, Farringdon, end. Known as the General Market, these make up about a quarter of the whole. This is now the target of office-block developers, with the active assistance of the freeholders (and planning authority), none other than the City of London Corporation. The City - which does not represent the whole of London, rather the famous "Square Mile" that is essentially London's financial district - loves offices. It cannot get enough of them.

The General Market is a late work of architect Sir Horace Jones, also responsible for many of the other City markets and Tower Bridge. Largely disused and distinctly neglected, stepping down the hill beside the Victorian flyover of Holborn viaduct, the General Market is one of those corners of old London that you can just imagine being colonized by the stalls, shops and restaurants that have transformed other such corners of the capital such as the ancient Borough Market by London Bridge, Leadenhall Market right in the heart of the City, or Spitalfields Market out east. Or for that matter the touristy Covent Garden market, a famous conservation victory of yesteryear.

Just such new uses - real-life open-market regeneration - are spreading all around Smithfield, which as a consequence now feels very like Covent Garden felt in the 1970s just before the market traders moved out. So - now is not the best time to start knocking great chunks of it down, you'd think. But this is not how the City thinks. The City is keen to have a large supply of available office space in order to maintain its world domination as, well, a place full of offices. There is a glut of empty office buildings right now, but it always wants more because it knows that, in the end, they will all get occupied. It thinks that 100,000 new financial-sector jobs are heading its way and it wants to house them. And the City is running out of places to build them. Hence the new crop of skyscrapers now being planned. And hence the big guns now being turned on Smithfield.

The big guns in question, apart from the City itself, are developers Thornfield Properties (part-owned by international financiers Lehman Brothers and the Bank of Scotland) with architects KPF -one of those transatlantic firms that builds all over the globe. Actually KPF aren't bad as corporate spacemongers go. They have a slick product, which you will find from Chicago to Shanghai. The two big blocks they propose, with their muscular raking columns and curving rooflines, are by no means the worst of their kind. In cold planning terms, they plug a gap, bringing the scale of West Smithfield up to that of the big buildings along Farringdon Road. But this misses the point. The point being that this low-rise end of Smithfield is a characterful urban pause-point, a breathing-space in what already feels far too much like an office canyon. Fill this gap and a very important part of London's eccentric inherited townscape will become just another glacial corporate cliff-face. A kind of speciality retail mall is proposed at ground level in the largest new building. But you could turn the existing buildings into a speciality mall, if you weren't wanting a load of offices as well.

The General Market was built as part of a huge, technically advanced Victorian engineering exercise that includes railway tunnels and sidings underneath. Trains run through the basements of the buildings. It is said that this underworld is in a poor state, and needs to be rebuilt at a cost of £18m - which you cannot do with the old buildings on top. How convenient for the developers. However their own engineers have inconveniently pointed out that it is also possible to repair the tunnel structures perfectly satisfactorily - so long as you keep the old buildings.

Following a vociferous campaign by conservationists including Smithfield-based Save Britain's Heritage, it seems increasingly likely that the General Market will be "listed" by the government as being architecturally and historically significant. This however does not confer absolute protection: listed buildings can still be torn down. Sometimes this can be good. For instance I am glad that a group of listed Victorian buildings near the Bank of England - fiercely fought for by SAVE - finally made way for the great prow of Stirling and Wilford's deeply eccentric Number One Poultry building, the best piece of Post-modern architecture in London, looking better and better as time passes. At Smithfield, however, there is no equivalent of Stirling in the frame.

West Smithfield's situation reflects the eternal struggle of London: Mammon versus moderation. In truth the capital needs both. We need the great engines of finance and administration, in the right places. But we also need the quirky corners that make London different from everywhere else. Save and restore Smithfield's General Market buildings, and this unique urban oasis will be strengthened. Sweep them away in favour of internationalist office blocks, and future generations will curse us for allowing it to happen. It really is as simple as that.

Conservation action group SAVE: www.savebritainsheritage.org
Developers Thornfield: www.thornfieldproperties.co.uk
Hayes Davidson architectural illustration studio: www.hayesdavidson.com