Fundraising for Tate Modern extension reaches half-way point

"We've made some significant advances in terms of the sums we've raised this year, and we're now roughly speaking half way towards our target of just over £200 million," said Sir Nicholas.

Speaking at a press conference to launch Tate's annual report, Sir Nicholas announced that the extra cash raised this year, thought to be approximately £25 million, had come from "a number of sources both within this country and abroad".

"We continue to believe that there are many individuals with the capacity to help us and we continue to have discussions with them," he added.

In recent months Tate has carried out preparatory works for the extension to the former Bankside Power Station building, including the removal of the lids of the former oil tanks which will form part of the new building designed by Herzog and de Meuron.

Sir Nicholas gave a strong hint that the extension will not be completed by 2012 as he had originally hoped, but said that Tate will be making an announcement next spring about its programme for Olympic year.

"I am absolutely certain that we will have something for you to see in 2012," he said.

Tate Modern has also announced its exhibition programme for 2011. Highlights include a major retrospective of Joan Miro from April to September and autumn exhibition of Gerhard Richter to coincide with the artist's 80th birthday.

• On Saturday 18 and Sunday 19 September there will be an opportunity to see the oil tanks and building site close up as part of the Open House London weekend.

• On Wednesday anti-war campaigners staged a press conference and photo opportunity outside Tate Modern to protest against Tony Blair's book launch which had been due to be held at the Bankside venue.