Well they didn't use those words, but they did claim they could arrest him in the Ecuadorian Embassy: http://rt.com/news/assange-arrest-asylum-780/ And the police force they'd amassed at the building suggested they might be preparing to do so.Incidentally they didn't threaten to storm the embassy.
To be honest I would be more worried about Swan telling the RBA to sell the Gold to meet the deficit gap... there's no reason to keep our Gold in London unless planning to sell or lease it.