Politicians and bureaucrats don't pull an eye-popping wage (although they often make up for it in expenses) – what they mostly live for instead is power. Everyone who's anyone, therefore, wants to be at this week's Group of 20 meeting. The trouble is space is limited. Well, kind of. If it were as simple as inviting the top 20 richest countries based on gross domestic product say, Belgium, in 21st spot, would no doubt understand. Who knows, it may well pip Poland next time.

But the guest list is complicated. There are no formal criteria but the composition of the group is unchanged since it was established a decade ago. Very broadly, economic size matters. But Spain and the Netherlands are not members in spite of being ranked 11th and 18th respectively based on International Monetary Fund estimates for 2008 output (although both countries have been invited to London). Far smaller South Africa and Argentina, on the other hand, have always been part of the cool gang.

In the G20's own words, members must have “systemic significance for the international financial system”. Hence oil rich Saudi Arabia is a member. But where is Switzerland (not a member, not invited) or the United Arab Emirates (ditto), both important to global finance? Equally, the G20 aims to be geographically balanced and reflective of population. Here the group succumbs to tokenism or fails completely. Thailand and South Africa may be far flung on the map, but are hardly big hitters of geopolitics.