The Home Office has apologised to Chinese artist Ai Weiwei and said he will be issued with a full six-month visa after lengthy wrangle.

The artist, famous for designing Beijing's Olympic stadium and filling Tate Modern's Turbine Hall with ceramic sunflower seeds, is travelling to London for a landmark exhibition of his work after Chinese authorities granted him a passport.

A Home Office spokesman claims Home Secretary Theresa May was not consulted after Mr Ai was initially refused a visa.

He said: "The Home Secretary was not consulted over the decision to grant Mr Ai a one-month visa.

"She has reviewed the case and has now instructed Home Office officials to issue a full six-month visa.

"We have written to Mr Ai apologising for the inconvenience caused."

The Royal Academy of Arts chief executive, Charles Saumarez Smith welcomed the decision.

He added: "We look forward to welcoming him at the Royal Academy for the opening of his major exhibition in September."

Ai's passport was seized by the UK authorities when he was arrested in 2011 during a government crackdown on political activists.

He was held over alleged crimes of bigamy and tax evasion, but was released without charge.

Ai was fined the equivalent of £1.55 million for tax evasion in 2012.

However, he lost his appeal agains the fine and said it was politically motivated due to his criticism of the Chinese government.ment.

On the social media site, Instagram, Ai stated at the time he had never been charged or convicted of a crime."

He said that he had attempted to clarify this claim with the UK Visas and Immigration Department and the British Embassy in Beijing several times by phone.