Could be dietary related too, or factors relating to multiple generations of families cohabiting. That said, these are prevalent in the sunny parts of Asia too, which doesn’t appear to be suffering so much, so my suspicion would be Vit-D related.

South Asians and East Asians are pretty different genetically, so the lack of distinction really doesn't help.

In the UK Asian == South Asian

Source? I've never got that impression as an English person. I consider it to be non-specific. However, if you're in a place like Southall or Bradford then the "Asian" people around you are indeed more likely to be south Asian.

But Indian/Pakistani aren't dying at much higher rate in their own country or are they? I've no data.

I would imagine that the sun is hotter and shows itself more often in India and Pakistan - hence the darker complexion.

Much easier to have a vitamin D deficiency in Britain than in India/Pakistan because there is so much less sun.

Very likely it explains at least part of the difference.

Because obviously people with darker skins produce less vitamin D naturally and are more vitamin D deficient and all indications are that vitamin D deficiency is a big factor in Covid19 morality.