The economy grows if there are more people in it. GDP is just all economic activity summed, so adding more people inherently grows GDP, which is what is usually

The economy grows if there are more people in it. GDP is just all economic activity summed, so adding more people inherently grows GDP, which is what is usually meant by "the economy". This obviously doesn't automatically mean everyone gets richer though, it just means more economic activity is now being counted under the UK vs other countries. This sort of immigration driven "growth" is sort of like a child "growing up" by getting fatter - yes it's definitely larger, but that doesn't mean healthier. From the perspective of the average British person, merely having more people around doesn't inherently make things better even if GDP has gone up, and can practically make things worse if it happens too fast as there's a limit to how fast infrastructure can be built. People who view the world exclusively via spreadsheets may struggle to understand this basic point, but everyone else can see it quite clearly.