We will certainly see a degradation in our standard of living if we are all sitting around collecting OAP with nobody working.
And how is this helped by importing immigrants without the requisite skillset to command sufficient salaries that they are actually paying taxes, as opposed to consuming services like health care which others must pay for?
It's pretty simple to get your head around, if we aren't having babies then we need immigration.
We don't need as many as we are getting. Our population would be stabilized with 100k, and we should be doing our best to get those who are going to pay taxes and adapt well to our culture and values.