He’s added quite a few himself mind you …
https://www.boris-johnson.com/2007/10/25/global-population-control/
It is time we had a grown-up discussion about the optimum quantity of human beings in this country and on this planet. Do we want the south-east of Britain, already the most densely populated major country in Europe, to resemble a giant suburbia?
This is not, repeat not, an argument about immigration per se, since in a sense it does not matter where people come from, and with their skill and their industry, immigrants add hugely to the economy.
Except what happens in the south-east of Britain really is a conversation about immigration, because the total fertility rate of the UK’s population is way below replacement level, particularly if we exclude migrants from the calculation.
Conclusion - Johnson is not very bright, or he was just virtue signalling to the people in the media so they wouldn’t oppose his election. In short, he’s either a liar or an idiot, or a bit of both.