As the leaders of the 53 Commonwealth nations gather at Windsor Castle today, the Queen can reflect with quiet satisfaction on a job – her job – well done. She has presided over the largest gathering of Commonwealth Heads of Government in history, and they seem likely to approve her wish that her son, the Prince of Wales, will succeed her as head of the organisation. This is a remarkable achievement.

Established by King George VI as a sort of nostalgic gathering of former British colonies, the Commonwealth is an unlikely gathering of countries from around the world. For much of its existence, the organisation has been treated as utterly peripheral by successive Labour and Conservative prime  ministers – sort of Royal oddity that had little to do with the real world. This sense was increased, but not caused by, Britain’s membership of the European Community/Union.

The size and global reach of the Commonwealth as we have seen it this week is a testament to the Queen’s stubbornness and persistence. The Commonwealth was established by her father and it mattered to him. Because it mattered to him, it matters to the Queen – she is devoted to the memory of her father. So, over the course of her long reign, she has steadily grown the Commonwealth from a small grouping of barely half a dozen member countries to a massive global organisation.

After decades of British political indifference, all of a sudden the Commonwealth has become a centre piece of post-Brexit trade policy. Like all the best plans this one has come about by accident. This week’s conference was never meant to be hosted by Britain at all. It was meant to be hosted by Vanuatu, but a cyclone struck and made that plan impossible. So Britain, reluctantly, stepped in. With Brexit driving a coach and horses through 40 years of established foreign and trade policy, Britain has suddenly been presented with an extraordinary global network to reach (back) out to.

This great unexpected, unplanned, extraordinary opportunity came about because the Queen would not be put off by domestic political indifference. She, and the Duke of Edinburgh let us not forget, have devoted their time and energy to building up this incredible global network, by themselves and on their own initiative.

The Commonwealth is an extraordinary testament to the Queen’s foresight and eye for an opportunity. Fond of the Queen these global leaders may be, but they have not travelled from across the globe to eat a cucumber sandwich at Buck House. They have come because they see a point to the Commonwealth. Now, the challenge for Britain is to prove them right.