Mr Johnson walked around 10 stalls pitched outside No 10 on Monday, sampling wares at the event held to showcase British trade.
The Prime Minister hailed British food as “the best in the world” in a speech outside his official residence before enjoying a cup of tea and chatting with stallholders.
“A fantastic effort by British food and farming… but there is still so much more we can do,” he said.
“What’s happening in the world, we’re facing huge pressures caused by the energy spike, the spike in the price of energy.
“That’s having a knock-on effect on food. The world needs more food, the world needs more cheap food, and the UK needs more cheap food as well, doesn’t it?”
“Let’s export ever more UK food,” he added.
The Prime Minister took part in candle-dipping at a stall held by St Eval candle company and operated an electric weed-zapper showcased by the Small Robot Company, remarking: “Spooky.”
International Trade Secretary Anne-Marie Trevelyan and Business Secretary Kwasi Kwarteng were among others to attend the event, along with business owners and their constituency MPs.