Theresa May delivered a defense of free trade on Monday, although she added that more could be done to make the global system fairer.
Speaking at the Commonwealth Business Forum in London, the British prime minister said "global growth is fragile."
"While we should be unapologetic in our support for free and inclusive trade, we should also work hand-in-hand with businesses to make it more efficient (and) more effective," she said.
"Playing fields can be leveled, barriers removed, the benefits opened up to all… The challenges posed by protectionism are all too clear."
The Commonwealth is a 53-nation bloc consisting of the U.K. and its former colonies, including India, Canada, Singapore and Nigeria. It encompasses 2.4 billion people and in 2017 had a combined gross domestic product (GDP) of $10.4 trillion.
Some groups have proposed that increasing trade with the Commonwealth is an important option for the future of the U.K. after it leaves the European Union.
Currently, the Commonwealth accounts for a small part of U.K. trade. Roughly 9 percent of total U.K. exports went to the Commonwealth in 2016, dwarfed by the 43 percent that went to the EU.
Meanwhile, the Commonwealth provided around 8 percent of the U.K.'s imports, roughly the same as those coming into the U.K. from China.
Intra-Commonwealth trade in goods and services rose to $560 billion in 2016, although this only accounted for 20 percent of the member countries' total global trade. The figure is expected to reach $700 billion by 2020.
In her speech, May said: "The best way to raise living standards for all is through economic growth based on free enterprise, operating in inclusive, fair and open rules-based markets."
"Freer, easier trade means stronger economies, more jobs, more choice and lower prices," she added.