Open Door Immigration.

It is fully logical to accept that, on a small group of islands such as the UK, there must be a point when migration to the country has reached a level when further population increases are 100% unsustainable. 
Those of the left who advocate adding to those burgeoning numbers make no comment. 
There is already an official population of around 62 million  which is almost certainly closer to 66 million - which makes us one of the most crowded places on the planet. We do not have the space of a Canada, a Brazil, an Australia or even the USA.
So. Here is the question for the fling-the-doors-open left. How many more migrants must we absorb before you choose to consider common sense? - Is it one million? Is it maybe, ten million? Perhaps a hundred and fifty million? TELL US!
There is not the shadow of a doubt that more than a 150 million people would opt to come here given the opportunity.
Virtually all would be unskilled. Many would not know any English. So. No possibility of societal breakdown?
Come on you lefties all - TELL US YOUR FIGURE!