The Royal Festival Hall's neighbour on the South Bank, petrol giant Shell, has pledged £1 million towards the renovation of the concert hall.
"With the help of our funding partners, the work we are undertaking will ensure that the Royal Festival Hall, one of London's greatest cultural assets, will be fit to meet the demands of our public in the 21st century, alongside its peers in other world-class cities," said South Bank Board chairman Lord Hollick.
James Smith, Shell UK's chairman, added: "As neighbours, we are delighted to be able to support the transformation of the Royal Festival Hall, one of the most important cultural centres in London."
The Festival Hall is due to close for 18 months of refurbishment in July, during which the arts programme will continue in the Queen Elizabeth Hall next door, and reopen in early 2007.
Other building work is also under way, including the opening of new shops (including Foyle's) and cafes by the riverside entrance this summer and a new office building alongside Hungerford Bridge.