Published last month, the United Nations working group's non-binding legal opinion was instantly dismissed as "ridiculous" by London, which has now submitted its formal response, inviting the panel to reconsider its conclusions.
Assange faces a rape allegation in Sweden but has been inside Ecuador's embassy in London for nearly four years in a bid to avoid extradition.
The 44-year-old Australian fears that from Sweden he could be deported to the United States over WikiLeaks' release of 500,000 secret military files.
"The working group's opinion is deeply flawed and Mr Assange has never been the subject of arbitrary detention," the Foreign Office said.
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"His human rights have been protected throughout."
Anti-secrecy campaigner Assange initially spent 10 days in a London prison having been refused bail, but his detention was "absolutely in line with the relevant legislation and regulations", the statement said.
The former computer hacker's series of failed court appeals against extradition to Sweden took 18 months and "cannot be considered excessive or unfair", the rebuttal said.
The UN panel said Assange should be able to claim compensation from Britain and Sweden.
Assange hailed the findings as a "victory", but has continued to remain in the Ecuadoran embassy.
The working group will consider Britain's response on April 18 in Geneva.
Foreign Office minister Hugo Swire said: "The original conclusions of the UN working group are inaccurate and should be reviewed.
"We want to ensure the working group is in possession of the full facts. Our request for a review of the opinion sets those facts out clearly.
"The UK continues to have a legal obligation to extradite him to Sweden."
A hero to supporters and a dangerous egocentric to detractors, Assange founded WikiLeaks in 2006 and has been portrayed in two movies in recent years.