The EU is the biggest export market for almost every single one of the UK's 62 cities
The EU accounts for 46% of all cities' exports, making it three times larger than the USA and 11 times larger than China, the report said.
In total, cities accounted for 62% of Britain's total exports in 2014.
London was the largest exporter, responsible for just over a quarter of all of the nation's exports to other countries.
"While this of course is a static picture, to make up even a 10% drop in current levels of UK cities' exports to the EU would require more than a doubling in trade with China or increasing trade with the USA by nearly a third," the group said.
"And the variation seen across cities means that those negotiating the Brexit deal, as well as trade deals with other countries, will need to consider the geographical impact of the deals struck."
Here is the graphic:
Prime Minister Theresa May has laid out plans to take the UK out of the EU's Single Market in return for greater control over immigration. In a recent trip to the US, May emphasised the importance of new trade deals with President Donald Trump, who campaigned with the slogan "America First."
Alexandra Jones, Chief Executive of Centre for Cities said: "Securing the best possible EU trade deal will be critical for the prosperity of cities across Britain, and should be the Government's top priority as we prepare to leave the single market and potentially the customs union."
"While it's right to be ambitious about increasing exports to countries such as the US and China, the outcome of EU trade negotiations will have a much bigger impact on places and people up and down the country," she said.
And here's the EU export chart:
