It's not an assumption. The article stated that non domiciled residents DO pay a lot of taxes. That's why the UK is concerned that they are leaving and modelled

It's not an assumption. The article stated that non domiciled residents DO pay a lot of taxes. That's why the UK is concerned that they are leaving and modelled against that risk. I did a quick check and it seems like non dom's are about 0.11% of UK residents and pay about 1.24% of UK taxes. And this doesn't account for indirect benefits such as taxes paid on wages they generate.