In his YouTube talk of September 7 the RSGB General Manager quoted 3 million as the number of radio amateurs worldwide but where did this number come from ?

A figure of 3 million has been widely quoted over the last 20 years and is the figure that was published by the IARU in 2000.

In the last century the IARU used to regularly collect statistics for the number of radio amateurs in each country and IARU published these amateur radio operator global totals:

2000 - 2,986,772
1995 - 2,646,000
1990 - 1,967,000
1985 - 1,489,000
1980 - 1,134,000
1975 -   737,000
1970 -   525,000

Unfortunately IARU stopped collecting the data just at the point when amateur radio numbers started to decline.  Data is available elsewhere for a few of the larger amateur radio countries and except for the USA this shows a steady decline in radio amateurs since 2000. For example the number of amateur radio stations in Japan has fallen by over 600,000 in the past 20 years, see Amateur Radio Licensing Statistics at
http://ah0a.org/AH0A.html

In some countries there are separate operator and station permits, Japan is one such case. The Operator total given in the AH0A table is for all the amateurs that have ever lived since the 1950's. They are not all still alive or even interested in the hobby anymore. A better indication of numbers is provided by the Station license totals.

So how many radio amateurs are there in 2021 ? The answer is no-one knows but it's likely to be closer to 1.75 million than to 3 million.

IARU Amateur Radio Statistics
https://web.archive.org/web/20020612083455/http://www.iaru.org/statsum00.html