Traditionalists fear Smithfield will be devoured by developers

Three centuries ago, Sir Christopher Wren took London's Smithfield area lavishly upmarket by giving it a neo-Venetian canal, complete with elegant hump-backed bridges.

This week, the same trendy swathe of the capital will again burst into the architectural spotlight - but this time with an unseemly row that will reopen the battle between traditionalists and modernisers.

Almost two decades after Prince Charles's "carbuncle" tirade against a modernist National Gallery extension proposal, the bottom end of Smithfield Market, famed for its meat produce, looks set to become the latest planning war zone. At the centre of the controversy are three 19th-century market buildings that, by the late 1990s, had been rendered obsolete - and a demand for another 20 million square feet of office space in the City in just over a decade.

Plans set to be revealed tomorrow will turn the conservation area buildings, designed by Sir Horace Jones, into 80,000 square feet of glass and steel medium-rise rental units.

Commercial developers, Thornfield Properties, has hired Kohn Pedersen Fox - the firm responsible for the controversial 42-storey Heron Tower in London - to tackle the project. Prince Charles is against the Smithfield redevelopment. So is SAVE Britain's Heritage.

English Heritage, which fought the Heron Tower, is keeping its powder dry. But planners at the City of London Corporation, which owns the site, are poised to grant permission for the office block.

Generating about £4 million a year in rental income, the new building would erase a problem site forever, and contribute rates and site-leasing fees to the City's coffers. The brouhaha at Smithfield compares with the row over the equally fraught Spitalfields redevelopment two years ago.

There, Lord Foster designed a huge mixed-use building which cascades northwards from just behind Bishopsgate. Construction is underway, despite public and professional protest which included pungent criticism from Will Alsop, currently Britain's most high- profile architect.

At Spitalfields, redevelopment followed the construction of a large, super-modern glass and steel office block.

If Thornfield Properties, backed by the Bank of Scotland and Lehman Brothers, gets its office block at Smithfield, it could lead to the rest of the market being redeveloped when its lease expires in a decade. Smithfield remains "one of the great Victorian market complexes," said Dr Richard Holder, senior architectural adviser to the Victorian Society. "It would be near-criminal to damage the cohesion of the complex, which is one of the largest market areas in the country."

The site forms the western end of Smithfield, whose functioning market buildings lie above it, stretching 200 metres. "The scandal of the situation," said Adam Wilkinson of SAVE, "is that viable schemes for re-use of the buildings exist."

The Corporation of London invited consultants, Urban Space Management, to come up with ways to revitalise the General Market and Annexe. But their mixed-use proposal was abandoned. The question of viable alternative developments is thorny. The buildings lie over the Thameslink rail tunnel and the base of one of them, the General Market, forms a section of the tunnel's roof.

Greg Williams, spokesman for the Corporation of London, said: "We're as aware as anybody else of the charm and historical status of Smithfield. But in the next 12 years, the City needs another 20 million square feet of office space, and at least 90,000 more workers."

It is conceivable that KPF's structure - kept closely under wraps until next week - will set a decent new benchmark in the architectural killing field known as Farringdon Road.

And when the Clerkenwell Biennale - London's first international architecture-fest - opens with a staged cattle-drive through Smithfield streets, the 179 architectural practices that make the area London's undisputed designer hot-spot may reflect the fact that architectural glory is ruthlessly fleeting.