Mr. Ai, who was a design consultant on the Bird’s Nest stadium in Beijing and exhibited his sculptural installation “Sunflower Seeds” at the Tate Modern in London, was detained in 2011 while trying to fly to Hong Kong from Beijing. He was held and interrogated for 81 days and later prosecuted on a charge of tax evasion. A court ruled against him and said his studio owed $2.4 million in penalties and back taxes.
He has said the case against him was retaliation for his political activism, including his memorializing the thousands of children who died in schools that collapsed during a 2008 earthquake in Sichuan Province.
He said on Wednesday that the authorities had given him no indication of why he had received his passport now. “I only can say why not? They have promised for the past four years to give it back. Now finally they gave it to me,” he said in a telephone interview. “They always say it’s in the process but I just need to be patient.”
The confiscation of his passport meant that Mr. Ai was forced to organize his overseas exhibitions remotely, including shows at the Hirshhorn Museum and Sculpture Garden, part of the Smithsonian Institution in Washington, and at Alcatraz, the former prison in San Francisco Bay.
In addition to being unable to travel outside China, he was barred from holding shows in the country. His works were also removed from group exhibitions in Shanghai last year. But last month, he was allowed to open his first solo exhibition in China, an indication that the restrictions on him had begun easing.
Mr. Ai, 57, said he planned to travel to Germany soon. He has a studio in Berlin, and his son, Ai Lao, 6, has lived in the country for the past year with the boy’s mother. He said he also planned to get a medical examination. He underwent emergency brain surgery there in 2009 after he was hit in the head by a police officer in the southwestern Chinese city of Chengdu.
“I will apply for a visa, and I will take a trip as soon as I get a visa,” he said.
He said he was looking forward to arranging overseas art shows on site. Last week, the Royal Academy of Arts in London began a fund-raising drive to install eight of Mr. Ai’s reconstructions of dead trees.
Mr. Ai also turned his years without a passport into an art project, filling the basket of his bicycle, which was locked outside his studio in the Caochangdi district of Beijing, with flowers each morning. He posted the photographs online, and then reposted images of flowers that supporters had directed to him. He noted that Wednesday was his 600th day of placing flowers since he began the project in 2013.
LONDON — The Chinese artist Ai Weiwei has been denied a normal six-month business visa by the British government, which said on Thursday that Mr. Ai had lied on his application by neglecting to declare that he had been convicted of a crime.
Instead, Mr. Ai, who has a major art installation opening in September at the Royal Academy of Arts in London, was given an exceptional visa that allows him to remain in Britain from Sept. 9 to 29. That limitation means he will have to leave the country before the Chinese president, Xi Jinping, arrives for a state visit in October.
Mr. Ai is one of China’s most famous contemporary artists, but he has run into significant trouble with the Beijing government for his irreverence and his sometimes audacious protests. He was prevented from traveling abroad for four years, and got his passport back from the Chinese authorities only last week.
He denied lying on his visa application, and said he had never been convicted of a crime. His former lawyer, Liu Xiaoyuan, told The Associated Press in Beijing that a tax case was brought against a design firm that Mr. Ai is affiliated with, but not against him personally, and that although a fine was imposed, the matter is not criminal and has not been fully adjudicated.
A British Foreign Office spokesman denied that there was any connection between the decision on Mr. Ai’s visa and Mr. Xi’s state visit. After Mr. Ai protested the denial of the visa on social media, the Home Office said in a statement: “All applications are considered on their individual merits and in line with the relevant legislation. Mr. Ai has been granted a visa for the full duration of his requested dates of travel.”
Even so, there was immediate speculation that the British government, which has emphasized close economic and trade ties with China in an effort to increase British exports, had acted to ensure that Mr. Ai would not be in Britain at the same time as Mr. Xi and so could not embarrass him there.
Prime Minister David Cameron of Britain has been criticized for an overly mercantilist foreign policy at the expense of human rights. After the Chinese reacted strongly to his meeting in May 2012 with the Dalai Lama, Mr. Cameron had to cancel a visit to Beijing planned for a year later when he was told that no Chinese leader would be free to see him.
Pressed by the chancellor of the Exchequer, George Osborne, Mr. Cameron distanced Britain from the Dalai Lama and other controversial issues involving China, and he had little to say last year about what many regarded as a violation of China’s agreement with Britain to protect democratic rights in Hong Kong.
Mr. Cameron then infuriated the Obama administration in March when he decided to have Britain become a founding member of China’s new development bank for Asia, the Asian Infrastructure Investment Bank, considered a rival to the World Bank. Britain was soon followed by other important American allies.
Mr. Ai, 57, whose passport was confiscated in 2011 when he was detained for 81 days, flew on Thursday to Germany, where his six-year-old son lives in Berlin. Mr. Ai said Germany had given him a multiple-entry visa good for four years.
Before he departed, Mr. Ai posted on his Instagram account the British letter about his visa, the visa itself, and his responses. The letter said that “it is a matter of public record that you have previously received a criminal conviction in China, and you have not declared this,” but went on to say that “an exception has been made in this instance.”
Mr. Ai has emphasized in interviews that he was never formally arrested and that the tax case was brought against his design firm, Beijing Fake Cultural Development Ltd., and not him personally. His wife, Lu Qing, was the legal representative of the firm at the time of the tax case.
“It’s not on me, it’s on the company,” Mr. Ai said last week.
A statement posted to Mr. Ai’s Instagram account, which included a photo of a toilet, said that he had tried to clarify his record in several telephone conversations with British immigration and embassy officials. They “refused to admit any misjudgment,” the statement said.
“The decision is a denial of Ai Weiwei’s rights as an ordinary citizen, and a stand to take the position of those who caused sufferings for human rights defenders,” the statement said.