The flags are fluttering along the world's most famous mall.

Heavily armed officers patrol the Buckingham Palace precinct.

Occasionally a siren heralds the arrival of another motorcade, as leaders from the Commonwealth of Nations assemble in the heart of London for CHOGM.

Pronounced CHOG-UM, the Commonwealth Heads of Government Meeting is probably best described as the political equivalent of the Gold Coast's recent games.

The view from Westminster Square, London, in the lead up to CHOGM. ( ABC News )

It's a grand, diverse post-colonial conference of countries that are (mostly) united by a common past — the British Empire.

At first glance the stats suggest the 53-nation club is an impressive beast.

Home to 2.4 billion people, spread over six continents, it accounts for about a fifth of the world's trade.

But the Commonwealth is divided, not just by geography and GDP, but values too.

For example, gay and lesbian relationships are outlawed in the majority of member nations and some have long argued the whole gathering is a relic of a lost age.

Behind the pomp and ceremony of this diplomatic extravaganza, critics will inevitably ask:

What is the point?

Australia will probably use the forum to chat with leaders of island nations about China's long-term strategic plans, in particular its funding of roads and ports in the Pacific.

The Commonwealth is, of course, one club Beijing isn't part of.

There are suggestions India, the giant of the group, might also enjoy China's absence and try to project its world view.

There are suggestions members of the old empire are underutilised trading partners. ( Reuters: Adnan Abidi )

Long seemingly reluctant to fully engage in a forum that was such an obvious reminder of its colonial past, the country's Prime Minister Narendra Modi has decided to attend for the first time since 2010.

In Britain, CHOGM will inevitably be at least partially viewed through the lens of Brexit.

Ever since the EU referendum was promised, parts of the Eurosceptic UK press have run stories suggesting members of the old empire are underutilised trading partners, keen to renew ties with the mother country.

While several of the smaller nations can be expected to band together in groups to campaign for their respective concerns, like limiting plastic pollution or climate change in the Pacific and boosting wildlife conservation in Africa.

How long will the Queen lead the Commonwealth?

But one of the more interesting elements of the whole show may be the long-running, ongoing discussion about leadership, not achievements or goals.

As everyone knows, Queen Elizabeth II is elderly.

Her position as head of the Commonwealth isn't hereditary and not everyone is particularly excited about the prospect of Prince Charles taking over.

A few even think Her Majesty's replacement should be directly elected and preferably someone from a small nation, so the group can lose its white, colonial image.

But several countries, including Australia, think it makes sense to keep giving the title to the monarch.

The future Kings of England, Charles, William and George, are always likely to have more star power and possibly more spare time than someone like, Anote Tong, the former President of Kiribati.

CHOGM may consider the Commonwealth's leadership. ( Reuters: Lukas Coch )

Whatever happens though, this is fairly likely to be the Queen's last CHOGM.

Her Majesty avoids long-haul flights and probably won't attend the next gathering in Malaysia.

So, if nothing else, we can expect all leaders to pay heartfelt tributes to a ruler, who has arguably done as much as anyone else to unite the Commonwealth and keep it going throughout her long reign.