Just a few months after being elected Conservative Party leader, David Cameron flew to Rwanda. It was a high-profile trip so he could see first-hand the development of one of Africa’s fastest-growing economies and launch his party’s review on globalisation and global poverty.

On his first day, he visited a textile factory in Kigali, the country’s capital. Above the hum of the silk reels, he chatted to some of the workers and admired the quality of the patterned fabrics. Before he left, the factory owner, Raj Rejendran, asked for a word.

Growing the business, he explained, required expanding into overseas markets. He knew there was demand in the UK for his silk fabrics, but he faced heavy import duties. Might the new party leader look into the issue? David Cameron promised to do what he could.

Since becoming leader he had made tackling global poverty a personal priority. He had even put Africa’s interests above those of his own constituents, heading to Rwanda when thousands of homes in his Oxfordshire constituency were under floodwater.

But there was little help the Tory leader could offer Mr Rejendran or any other African entrepreneur who wanted to reach British customers. That’s because the UK’s import duties are set in Brussels, not London.