According to the Office for National Statistics (ONS), in the year ending June 2020, an estimated 673,000 people emigrated from the UK. This includes both UK-born and non-UK-born individuals. Of the total emigrants, approximately 316,000 (47%) were UK-born, and approximately 357,000 (53%) were non-UK-born. The non-UK-born emigrants included both non-British citizens and British citizens who were born outside the UK.

So it's almost 50/50. Looks actually worse than I'd imagined.