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