It may have to do with tax credits while the film was being made, followed by Lucasfilm indicating that it's under United States copyright law.
The Department for Culture, Media and Sport (where Vaizey is minister of state, with responsibility for culture, communications and creative industries), is ultimately responsible for certifying The Force Awakens as a British film, and therefore gives it access to tax relief. For all its Hollywood pedigree, The Force Awakens must be certified as a British film for tax purposes, and like other Hollywood blockbusters – including The Avengers: Age of Ultron, Gravity and World War Z – will take full advantage if, as appears highly likely, it is successful.
All films receiving tax relief must pass the “cultural” test administered by the British Film Institute, which operates a points system, taking into account such factors as the proportion of the film set in the UK or Europe, the nationality of the lead actors and crew, and how much of the film’s dialogue is in English. However, thanks to its production base at Pinewood Studios in Buckinghamshire, a significant amount of UK crew, and its two British lead actors in Daisy Ridley and John Boyega, it is expected to easily pass the test.
So, basically, it was a UK film for the purpose of tax credits, but for the purpose of copyright, that's in the United States, with its different laws.