Some interesting figures
https://www.migrationwatchuk.org/key-topics/illegal-immigration


https://www.indexmundi.com/map/?t=0&v=21000&r=eu&l=en

"By its nature, illegal immigration is very difficult to measure. First, the Census does not record the immigration status of respondents and, in any case, most illegal immigrants would be very unlikely to respond. Moreover, in 1998 the then Labour government ended the system of exit checks on non-EU migrants which meant that for nearly 20 years, until their reinstatement in April 2015, it has been impossible to determine who is still in the country."

I wonder why supermarkets provide for a much larger population in the UK than the official figures suggest?
Answer: "In political terms, standing behind these figures would be to toss a hand grenade into a vat of gasoline. People would be hounded out of a job for scaremongering."

The Office for National Statistics' figures, published last week, predict a population of 75 million by 2051. It's an honest estimate but horribly wide of the mark because number counting doesn't work effectively. If you want to know how many there are of us, ask a food firm. (and some would suggest even their figures are conservative)
https://www.independent.co.uk/news/business/comment/city-eye-facts-on-a-plate-our-population-is-at-least-77-million-5328454.html