LONDON, Dec. 13 (Xinhua) -- British Prime Minister Boris Johnson said Sunday that Britain and the European Union (EU) remain "very far apart on key things" and Britain should get ready to trade with the EU on World Trade Organization (WTO) terms on Jan. 1.

Johnson made the remarks after he and European Commission President Ursula von der Leyen agreed to continue post-Brexit trade talks beyond Sunday's deadline.

Speaking to British broadcasters, Johnson said that he is "very happy" to speak with other European capitals. "We're going to try with all our hearts" for a deal, he said.

However, he said, "The most likely thing now is that we have to get ready to WTO terms -- Australia terms."

The EU does not have a free-trade deal with Australia, although they are in negotiations. The two sides operate mainly on WTO rules, with huge tariffs on imports and exports.

Britain should "get ready with confidence for January 1 -- trading on WTO terms if we have to," Johnson added.

The prime minister said Britain "certainly won't be walking away from the talks". However, he reiterated that Britain can't be locked into EU regulatory "orbit" after Brexit.

"The UK can't be locked into the EU's regulatory orbit and we've obviously got to take back control of our fisheries, so those are the points -- I think it's very clear what the UK is talking about," he said.

The British and EU leaders have said significant differences still remain between the two sides on three critical issues: level playing field, governance and fisheries.

The trade negotiations are at a crucial stage as time is running out for both sides to secure a deal before the Brexit transition period expires at the end of the year.

Failure to reach a free trade agreement means bilateral trade will fall back on WTO rules in 2021.