Not defending Mr and Mrs Sunak, which is another story, but the UK Domicile thing has been around for many years and no Govt, left or right, has ever attempted to change it.
The Brown administration (ie Labour) did change the rules so that it was no longer possible to somehow be "Not domiciled" in the UK and yet be in Parliament setting rules - including the tax rules - for the country you're supposedly not living in.
Several Tories decided that not paying taxes was better than sitting in Parliament and so they quit as a result of this.
