Leading article: Art, ambition and a reality check

The Tate's redevelopment project is suitably ambitious for the world's most popular museum of modern art. The gallery is planning an 11-storey edifice to sit next to Tate Modern's Turbine Hall on London's Bankside. This will house new galleries and performance spaces. The Tate's director, Sir Nicholas Serota, has spoken of his desire to establish a "cultural quarter" in the capital in time for the 2012 Olympics.

The Tate has already attracted 7m in funding from the London Development Authority and a 5m donation from the banker John Studzinski. And yesterday the Department of Culture Media and Sport said it will stump up 50m to bankroll the plans. This will be the Government's largest capital commitment to a cultural project since the construction of the new British Library.

This announcement is a good moment to take stock. The Tate has been a stunning success in the new millennium. Tate Modern hosts an astonishing four million visitors every year. And Tate has been successful outside the capital, too. The Liverpool gallery attracts 600,000 annually. All the organisation's claims of broadening access to the arts and benefiting the national economy by attracting tourists from abroad are legitimate.

But state funding, especially on this scale, cannot be a one-way street. It is inevitable and right that the Tate will come under greater scrutiny as a result of this funding announcement. The Tate often complains about the size of its acquisition budgets. This is to be expected; all cultural organisations would like to be able to buy more works for their collections. But the Tate's pleas for more resources should be considered in the light of this additional capital funding. We should also bear in mind that less than half of the Tate's permanent collection is on display at any one time. As a result of this development, the gallery will now have lots of space in which to display its present collection.

Perhaps it is also time for the Tate to consider splitting into two separate organisations. There has been an increasing divergence in recent years between the "British" operations and its focus on international contemporary art. The two objectives no longer sit together very well. The Tate has become an unwieldy empire. And the board of trustees has shown worrying signs of complacency. The organisation's ill-advised purchase of a work by Chris Ofili, who also happened to be one of the Tate's trustees, was embarrassing.

Competition and specialisation can be as invigorating in the subsidised arts as in the commercial world. The Tate brand has a bright future. But it is time to consider whether it would be brighter still if it split up its management.