For £45m you could commission a blockbuster building. But spend that same amount on a sprawling historic building and the money can be swallowed up on restoration, fixing leaky roofs and installing expensive new services and environmental controls; if the job has gone well, it can be hard to see what’s been done.
Tate is currently trying both. At Bankside, indeed, it is spending a lot more (£215m) on a pyramidal brick tower by Swiss architects Herzog & de Meuron, a striking structure to shore up the art space inside what has become the world’s most popular museum of modern art, Tate Modern. Along the river at Millbank, meanwhile, Tate Britain has quietly undergone a comprehensive £45m seven-year programme of careful renewal and change overseen by London architects Caruso St John.
in May alongside the acclaimed chronological rehang  of the works in the Tate collection and includes an entirely new gallery space dedicated to Henry Moore. The new phase, however, sees the reopening of the main riverside entrance and the reconfiguring of the entrance area and rotunda in a manner that transforms the space while maintaining its particular, stony-cold Edwardian character.
The entry sequence has been opened up and made lighter with new glazed doors and an elegant window by artist Richard Wright, all of which makes the river visible in a way it never was before. The most striking new feature, though, is a spiral staircase set into the centre of the rotunda – where the gallery used to erect its artist-decorated Christmas tree.
The stair is enclosed by a curved screen made using a decorative device derived from a pattern found on an original floor – where it once framed a fish pond framed by aspidistras. The stair treads themselves echo the curving form in a theatrical sweep that makes the journey down to what once felt very much like a second-rate space – the basement – feel grand and deliberate. If there is a criticism to be made it is that the mirror-polished handrails and spiralling glass look a little too sparkly, with a touch too much of the oligarch’s mansion about them.
The basement itself has been revamped, retaining the existing café with its vaulted ceilings and adding a new café space that spills on to a sunken terrace at the front of the building. A new vaulted ceiling has been created here and decorated with infinite care by artist Alan Johnston, whose delicate pencil work carefully articulates the individual vaulted segments.