Chinese government critic and dissident artist Ai Weiwei has been denied a business visa to the UK because of his criminal record, even though he has never actually been charged or convicted of any crimes.

Four years after his passport was confiscated by Chinese authorities, Ai got it back last week. He posted a jubilant photo on Instagram, before announcing his plans to visit Germany to see his young son, and to travel to London, where an exhibition of his work is launching in September.

However, his application for a six-month business visa was then rejected by the British embassy in Beijing. Ai will be able to stay in the UK for 20 days in order to attend his show's opening at London's Royal Academy of Arts, though he won't be able to supervise much of the installation.

"It is a matter of public record that you have previously received a criminal conviction in China, and you have not declared this," the letter read.

Ai is still allowed visit the UK between September 9 and September 29 this year, meaning he will just miss Chinese President Xi Jinping's state visit, scheduled for October.

Screengrab via Instagram

Ai was detained in China for 81 days in 2011, but never actually prosecuted or convicted. His design firm was later slapped with a $2.4 million tax bill, which he fought unsuccessfully in Chinese courts. The persecution was widely seen as punishment for Ai's outspokenness against the ruling Communist Party and its government.

After his release he was placed under a travel ban. It was partially lifted in 2012, allowing Ai to travel domestically, but authorities kept his passport on the grounds that he remained under investigation on suspicion of pornography and illegal exchange of foreign currency. Ai denied both charges, and he has not been indicted on either charge.

Chinese authorities often deny passports to dissidents who might embarrass the ruling Communist Party overseas.

The Communist Party has also been known to detain citizens for long periods without charge, most recently some 200 lawyers and activists who were taken in during what the authorities said was an attempt to "smash a major criminal gang."

Screengrab via Instagram

Before his detention, Ai had spoken out about a number of national scandals, including the deaths of students in shoddily built schools that collapsed during a massive earthquake in 2008.

Ai government has blacklisted him from any mention in state media, and he is not allowed to post anything on China's social media.

He was also barred from holding exhibits in China, but as a sign that the restrictions might be easing, Ai was allowed to hold his first solo exhibit in Beijing last month. He has held two more exhibits since then, also in the Chinese capital.

Royal Academy director Tim Marlow said the lifting of Ai's travel ban was wonderful news: "We are delighted to announce that he will be joining us as we finalize the installation of his exhibition."