Malcolm Turnbull has discussed trade and security with United Kingdom Prime Minister Theresa May before becoming the first Australian leader to plant a tree at her private retreat.
Mr Turnbull planted an English oak at Chequers Court, the country retreat of UK leaders, after a bilateral meeting with his counterpart on Saturday local time.
Other world leaders to have planted a tree at the historic residence include Dwight D. Eisenhower and Bill Clinton.
The two leaders addressed trade opportunities and cyber security over a lunch of fillet beef, turbot and poached rhubarb.
Ms May and Mr Turnbull spoke about their new cyber security agreement, under which Australia and the UK will work closely to deter and counter suspicious cyber activity.
The leaders also discussed a range of security issues, including North Korea, and Syria.
"Whether it is in chemical weapons, whether it is in the threat of terrorism, cyber security, you see so many challenges to the rule of law," Mr Turnbull told reporters.
"The maintenance of which is essential to not just our security, but our prosperity."
Mr Turnbull welcomed the increased UK presence in the Asia-Pacific, through three new diplomatic posts.
The leaders also agreed to future collaboration on science and innovation, in particular in universities.
