Assange's case would be referred to a judge and he could face a maximum jail term of one year, a spokesman for the state Crown Prosecution Service (CPS) told AFP.
The Australian sought asylum in Ecuador's London embassy in 2012 after a judge ordered his extradition to Sweden to face allegations of rape and sexual assault.
Police said a warrant was issued against Assange in 2012 after he failed to hand himself in, adding: "The Metropolitan Police Service is obliged to execute that warrant should he leave the embassy."
Assange insisted the claims were politically motivated, and feared that going to Sweden would result in his extradition to the United States over WikiLeaks' publication of classified US military and diplomatic documents.
The CPS spokesman could not confirm whether Britain had received a US extradition request.
"The UK government's policy is to neither confirm nor deny any request for extradition until and unless an arrest is made," he said.
The police ended their round-the-clock guard outside the embassy in October 2015, amid public criticism of the cost.
But they said they were strengthening a "covert plan" to prevent his departure.
On Friday, they said Assange was previously wanted for "an extremely serious offence" in Sweden and the police presence around the embassy had "reflected the serious nature of that crime".
"Now that the situation has changed and the Swedish authorities have discontinued their investigation into that matter. Mr Assange remains wanted for a much less serious offence," it said.
"The MPS will provide a level of resourcing which is proportionate to that offence," it added.
Assange was granted asylum by Ecuador and has been able to evade justice because he is on Ecuador's sovereign territory by being in the embassy.
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