The country does not need to maintain a steady population. It needs a declining population.
Be very careful what you wish for.
Population isn't just about the total: what matters particularly is, as the statisticians say, how it is broken down by age and sex.
I have said before, and I'll say it again. If you only ever look at one graph in your life it needs to be figure 4 here from the 2021 UK census:
Census 2021 rounded population and household estimates for local authorities in England and Wales, by sex and five-year age group.
www.ons.gov.uk
The trend of population ageing has continued, with more people than ever before in the older age groups. Over one-sixth (18.6%, 11.1 million) of the population in 2021 were aged 65 years and over, up from 16.4% (9.2 million) in 2011. The size of the population aged 90 years and over (527,900, 0.9% of the population) has increased since 2011, when 429,017, 0.8%, were aged 90 years and over.
Nearly two-thirds (64.1%) of the population in 2021 (38.2 million) were aged 15 to 64 years. There are more people in this age group compared with 2011 (when 37.0 million people were aged 15 to 64 years), but as a proportion of the overall population there has been a slight decrease in the size of this group (65.9% in 2011).
The remaining 17.4% of the population (10.4 million) were aged under 15 years. There are more people in this age group compared with 2011, however, as a proportion of the overall population, the size of the group has decreased (9.9 million, 17.6%, in 2011).
The UK has an unfunded state pension system, and a bulge of people in the 50-59 age group, approaching retirement (the "baby boomers"). Without a birth rate above replacement rate, and/or some inward migration, the ratio of economically active population to economically inactive population will plummet. Allow that ratio to fall too much and the UK state pension system and all of UK public finances will become unsustainable.
Unless you would like to work until you are 75?
If it isn't, the problem of caring for an aging population will become insignificant because the country will be increasingly unable to properly care for its younger members.
And with a declining population, who do you think is going to do this? I suggest that you take a look at what is happening in Japan and South Korea, where population is already declining.
What the graph shows is that the UK does not have enough people in two age groups: the under 5s and 15-24 year olds. Now is the time to rectify that with a higher birth rate and a bit of net inward migration, migrants predominantly being young adults. The UK population will start to decline naturally once the "baby boomer" generation starts to die in large numbers.
Figure 4 is usually called the population pyramid, and it needs to be shaped like that, with more people at the bottom than the top. When it starts to look more like a tree it is bad news.