For some countries bartering has long been a vital part of how they trade overseas.Read more
Szu Ping Chan
US President Donald Trump has said a "big" post-Brexit trade deal could happen between the US and the UK.
"Big Trade Deal is possible once U.K. gets rid of the shackles. Already starting to talk!," he tweeted.
Mr Trump is in the UK for a three-day state visit to the UK.