Looking at the plans for the proposed redevelopment of the Southbank Centre, two key questions come to mind. Will the proposals enhance the experience of those involved in the core creative work of the centre (those staging and performing in concerts, dance productions, films, talks and exhibitions), and will they make for better focus and enjoyment for the audiences and viewers? Will the architecture be improved and fit for the next 50 years or so? Does it measure up, for example, to the quality of the Royal Festival Hall?  My concern is that the Hayward Gallery, the Queen Elizabeth Hall and the Purcell Room would all be buried – not only under a lot of glass and steel – but also under a lot of confusion. Those buildings were designed in a complex, idiosyncratic way, with sculptural integrity. To try to tame this by sitting a shoebox on top of them seems destined to result in something like a dog's dinner. I am not in any way against the History House, the Children's House or the Word Space, but it seems a mistake to compromise our great institutions to fit them all in. Here is a wonderful central London site that has hosted the arts since 1951. If it is not working, let's make sure we either restore the original buildings with dignity, to make them as good as they can possibly be, or take the plunge and replace them with a 21st-century set of buildings, better suited to the art forms and audiences of today.  It's not the first time that a radical redevelopment has been proposed. Richard Rogers' 1994 plan to cover the entire site in a transparent sleeve was rejected for the good reason that it is very difficult to add a glass building to a concrete one without lots of bad junctions and lost spaces being created. The debate over the current scheme so far seems to have focused on the ousting of the skateboarders, but there are so many other things at stake.  There is no doubt that Jude Kelly, artistic director of the Southbank Centre, and her team have reinvigorated the site. It has continued to attract people from all over London, the UK and the world; 25 million people come to a cultural event at the Southbank Centre each year, and thousands more simply spend time there to be with others, in the company of the river Thames. It is great that this is a lively and lived-in space, but we need to think about its core purpose. There is a possibility that its very popularity is obscuring its primary functions.  What is great about the Southbank site as it was originally designed is that each of the art forms has its own discrete and distinctive building. The different venues are all laid out one after the other: National Theatre, BFI, Hayward Gallery, Queen Elizabeth Hall and Purcell Room, and Royal Festival Hall. You get a breath of fresh air and then pop in to your spot. There is a nice neighbourliness as well as a nature/culture dialogue happening when you go down to the river to see a play, listen to music, or see some art.  London has always had a love/hate relationship with this concrete architecture. This cluster of great brutalist buildings acts as both venue and object. The original LCC architects were a group with a common purpose, and as far from the species of "starchitects" as you can get. When you really look at the buildings, they have a quiet dignity and purposeful charm of their own. The designers had a very keen idea about social as well as topographical planning. They made a kind of tectonic architecture that works within the patterns of daily urban migration: they were, for example, thoughtful of the commuters flowing over Waterloo Bridge. They were interested in an architecture that mimicked geology, and wanted to keep a feeling of the notion of a river bank within the structure of the building. They thought that we would use the terraces and undercrofts like migratory seabirds use the cliffs of Hoy in the Orkneys.  Having enjoyed a lifetime of visiting inspiring shows at the Hayward Gallery, and having had the privilege of my own one-man show there in 2007, my feelings really focus on the Hayward and its status, function and identity. In the current proposal, the Hayward will be swallowed up by a great shared foyer. It will lose some of its exhibition space, be denied a clear external entrance and will have its unique sculpture terraces severely compromised. Presently, there is a wonderful contrast between the concentrated interior spaces and the release into the outside on those cantilevered trays that offer you long views of the city and the river. They are also very adaptable: think of the great way that they were used for the 2008 exhibition Psycho Buildings, when Gelatin, that energetic Austrian group of artists, flooded the southern court so that we could row out in small boats towards the London skyline.  Certainly, improvements to the gallery could be made. Provision could be made to exhibit the Arts Council Collection, our primary national collection of contemporary art. An education space and a seminar room would be good. There is no doubt that the Glass Box – the big glazed box that will provide an orchestral rehearsal space, proposed to sit between the Hayward, the Purcell Room and the shared central foyer – will make access to the gallery less direct and the building less distinct.  The Central Foyer will not necessarily mean clearer access for the public to the discreet functions of the Hayward. The gallery needs its own entrance, clearly identified as a building that stands alone. Presently, it functions as a unique place and has earned the love and affection of its public. The architecture is powerful and provides the impetus for strong ideas and clear, monographic shows. Denied any extra exhibition space or greater accessibility as part of these plans, it must at least be allowed to retain its separate identity. The plan does propose the restoration of the pyramid rooflights, which have been blacked out since shortly after the gallery opened. This will allow the natural light that was always supposed to grace the upper galleries to flood in again. The resulting clarity should be applied to the building as a whole.  The claim that the Glass Box will be the "third beacon" of the Southbank is questionable both because it is not of high architectural quality, and because its function is not adequately differentiated. To have such a massive effect on the whole area for the sake of a rehearsal space does not in any way seem justified. Architectural quality based on real need should be the criteria. What will it say to London and the wider world about our commitment to contemporary culture in all its forms? Unless great architecture is the aim, we will end up with a compromised hybrid that is not of equal quality to the National Theatre and the Royal Festival Hall.  Of course I want to see even more visitors enjoy an even greater level of activity. Of course I want artists to have all the space that they need. The true choice is either to demolish the existing buildings to make way for something better, or to respect the Hayward, Purcell Room and Queen Elizabeth halls as cultural instruments, needing sensitive improvement. These are landmark buildings on a landmark site. Great architecture rarely comes from accretion.
Built in 1951, the Southbank Centre is an architectural landmark that attracts 25m visitors a year. But will it survive another 50 years? Sculptor Antony Gormley on why bulldozing the site would be better than the planned revamp