But at the moment we know that in many respects there isn't the infrastructure. We certainly have a massive shortage of housing, and there appears to be a shortage of GP/health facilities. Our water infrastructure struggles to cope. etc. etc.
Since 1970 compared to other European countries there's been something like 4 million fewer homes built. Since the target of 300,000 new homes a year has been set it's generally been missed. Part of the reason for needing more homes is that average household sizes have been shrinking, so you need more homes to house the same number of people. This isn't anything which should be a surprise, yet many in politics don't want to deal with it as the loss of countryside is a vote losing issue.
The lack of GP's, at least in part, is down to government policy which means that it's better for a Brit to be a doctor in New Zealand than in the UK, so many younger doctors with less toys are willing to move there or to Australia and Canada. As to the actual buildings for them, developers can be made to build them or pay for improvements/extensions to existing centers, however it's not always used by local councils.
A lot of the issues with sewer systems not coping are down to the old combined sewers. A small part of this is that the water companies have to accept new connectors from developments, the government has provision in place to remove this right and has been talking about doing so for several years, it was suggested that it would be in place last year and now again this year. If that was put in place it would help with limiting the problems, as would several other things that the government could do.
However actually new developments aren't always the problem and sometimes can be the solution. Especially with the move towards water use neutral sites (i.e. reducing water use in areas so that the development doesn't increase the amount of fresh water being used, which in turn limits the amount of waste water which needs treating - it also often means delivery of rain water storage meaning less water entering the sewer systems, and with SuDS reducing peak flows to that of green fields the impact can be quite significant).
However, there's also a need for OFWAT to have some teeth so that the water companies do as they should do.
These are all things which need sorting regardless of if there's immigration or not.
However, arguably, sorting out infrastructure issues could be easier than providing solutions to other issues.
Sure, and IF we ever reach a point where the population starts falling below the capacity of our infrastructure, then there may well be a good argument to encourage immigration to take up that capacity. But that's not the case at the moment. Over the 20 years to 2022, the UK population increased from 59.4M to 67.6M - an increase of 14%. The UK population problem we need to solve today is that the population is growing more quickly than we can accommodate. Let's try to solve that before we worry about solving hypothetical problems that don't currently exist!
Again you're focusing on the totals and not how the numbers are split between the ages, yes we shouldn't have significant growth (some may argue an annual growth of 0.66% each year, which is the same as 14% over 20 years, isn't significant growth but that's a different debate), however we also need to better plan for a future with fewer working aged people compared to retired people.
There point which I'm making is (say) 1,000,000 a year is too high, but also 0 a year is also likely to be too low. The discussion is often polarised to those two options being the only options available, they are not, we could have (say) 30,000 a year, which would likely see small reductions in the total population but still see the working population being a bit more stable.
All in saying is don't get stuck into thinking that with zero immigration all the problems will go away, as since may ease but then others become more of an issue. It may well be that the new issues are now of a problem than the old, they may not. However, either way there needs to be better long term planning for them than there currently is.
At the very least something needs to be done about social care for older people, something which no government has really done much about since at least 1997 when it was acknowledged that it was going to be an issue going forwards and is a factor as to why there's been so many cuts to local services (not helped by central government cutting grants to local councils when they need even more money to provide the level of care needed due to an aging population).
Any adult coming into the country today is likely to be retiring before or soon after 2060, so it's very unlikely that encouraging more immigration today will help with a demographic problem in 2060! (At the extreme, if the retirement age stays at 67, a 20-year old at the start of his/her working life today will retire in 2071, but of course the average immigrant is older and so will retire sooner).
Indeed, however, the point I was making is that the 2:1 ratio would arrive much sooner with zero immigration. As not only do those immigrating bring their younger age compared to the native population they are also more likely to have more children than the native population (someone coming here in their 20's are more likely to have children than me, my parents or my grandmother), even if they don't have any more children there's a fair chance that they could bring children. The predictions are that school infrastructure is already too big and will only get larger compared to the number of children in this country (that's not too say that there's not a shortage in some areas, but that's offset by over provision in others).
However even then there's 2:1 ratio is just an easy to define point, it's likely to cause issues before then. Supporting 1 from 2.7 is easier than 2.6, and that's easier than from 2.5, etc. having zero immigration is only going to make those points come sooner and closer together. Meaning making tough choices sooner.
Yes, that is a potential concern and needs a discussion about what proportion of people being retired vs working we can support. But remember it's not just numbers of older people. For example, a big reason that the numbers of elderly is putting such a strain on the system is how many people spent their lives not exercising and not looking after their own health so they now need massively more care than they would have done. In the long term, that's fixable. There's also likely to be scope for how we change the way care is provided (more automation, more family support, finding ways for people to be less isolated, etc.). Some people who enjoy their jobs might prefer to retire later (which again helps with isolation). Those are harder things to sell politically and require more thought than just bringing in ever more people (who'll themselves eventually retire and need care and pensions) but will likely provide much more sustainable solutions (while also improving many people's quality of life into the bargain).
Indeed, however part of that is likely to mean people being passively active (by which I mean that is so much part of their daily life that they do it anyway), that's likely to mean more walking, cycling and public transport use rather than jumping in the car. For that to happen that's likely to mean more LTN, more ULEZ, more people feeling that there's a "war on motorists" and the like.
That's not something which is often attributed to the Tories (although to be fair they have brought into being Active Travel England and policies which will help if used properly), however more is likely to upset more of their base (especially with their shift rightwards). Especially given car ownership is seen as a mark of achievement and the subsidising of public transport requires more government spending (which has the perception of limiting the ability to provide tax cuts).
But there isn't suitable infrastructure now. And any demands on that which exists will be greater if more people are brought into the country to improve it. It needs to be improved by the numbers already here.
As I said, it's no use bleating over that. Ways will have to be found. If you said 60 years ago "climate change will be a real problem but we'll have to put up with it because we cannot stop burning coal" many people would have agreed with you. But it was no good simply saying that. Ways had to be found to live without burning coal (unless you live in China, India or the USA).
Then a health service free for all at the point of delivery might have to be one of the things that has to go the way of coal.
But there would be if the cake did not have to be divided into an ever increasing number of pieces.
The issue is not immigration per se. The issue is with the idea that the only way we can cure problems caused by an excess of people/lack of facilities (choose which one you prefer) is to encourage a greater excess of people. It's convenient when that excess is provided by immigration for its opponents to suffer the usual brandings (e.g. racists, bigots, xenophobes). But it doesn't matter where these extra people come from. We cannot adequately provide housing, infrastructure and the necessary public services for the people already here and that will not be cured any time soon (if at all)> So from the two preferences above we're stuck with an excess of people. A continually growing population - whether caused by immigration or by the people already here - will only make the problems worse and it is simply unsustainable.
Where have I said that we should have an ever increasing population?
What I've questioned (and if I've not been clear on this than I'm sorry) is that because the current level of immigration causes issues that the only option available is that we should have none.
That's not the case, by cutting immigration to zero there'll also be issues. For example seeing the population reach 45 million by 2100, which would (assuming an even distribution in the fall in population over time) could see the population fall from 67 million now to 61 million in 20 years time, however at the same time the rise in those over 65, 75, and 90 being already mostly baked in so will need to deal with the issues that having a smaller working population supporting them would bring (if the total population falls by 6 million and the numbers over 75 rise by, say, one million that's quite a shift in the ratio between working and non working).
The bottom line, should there be 0, 10, 100, 1,000, 10,000, 100,000 people per year coming here (with the linked question of what does the population numbers look like, as for at least most of those options that's likely to still mean a falling overall population size) and what are the issues that number will bring (be that from the need for more infrastructure or from a falling working aged population as a percentage of the total population) and how do we plan for that?
There's lots of other questions which need to be answered, however as the above should highlight there's a lot of space between a totally static population size and absolutely zero people from overseas moving to the UK (which by the way would include banning UK citizens from returning here, even banning all people born overseas would mean some UK citizens having to leave their babies or children abroad to move back here, even before you consider the impact on people who have married those born overseas).
Arguably there's one policy solution, from retirement you have a maximum of 20 years to live in the UK - but that would require having a way to ensure that maximum was adhered to and few would have the stomach to bring in a rule to kill people to enforce that.
(by the way, I'm not suggesting it as a serious suggestion, I only mention it as there was a sci-fi story one which did something similar where people would get a job on their half life aged 20 and they were killed off aged 40 to keep the population in check, and it would certainly deal with a lot of the issues that we have and will have - just not a very palatable one).