This is true. Immigration overall is declining... Also we need to get real, Illegal immigration isn’t unique to the UK, it’s a consequence of being a rich, stable country. All wealthy developed countries have it.
The USA has about 10-11 million undocumented migrants. Even tightly controlled systems like Dubai rely on huge numbers of foreign workers, but still have overstaying and people with irregular status. Poorer countries like Chad or Niger do not have illegal immigration because people do not want to go there.
So, yes keep trying to manage it, try different approaches, improve enforcement, check with employers and landlords, maybe bring in id cards ( except we seem to hate that idea and can't have it both ways). Control illegal immigration as best you can, but don’t see it as the single issue. It is not. Look at everything, distribution of wealth, environment, productivity, inflation, wages, economic growth, an ageing population, social care.
Do not fall for a self serving party led by a charlatan who has displayed hard wired racist and antisemitic behaviour since childhood, who has previously used false immigration fear mongering as an emotive trigger issue to manipulate a national referendum. If a politician wants you to focus on one issue above all others, it’s likely you are being manipulated.
Farage and Reform display so many red flags it is overwhelming. These include financial mismanagement, anti environment policies, express lies and manipulation, even occasionally revealing a true agenda to dismantle the NHS, replacing it with private healthcare. These red flags are accompanied by an underlying constant of breaking rules in order to feather their own nest.
So- we have always had, and always will have, some irregular immigration because it is a direct consequence of wealth and success. It is flawed to attribute illegal immigration as a sole issue, it is not the root cause of anything and everything you don’t like. Yes keep trying a variety of practical steps but also see it for what it is, one issue that is an inevitable consequence of our world ranking.