I'm finding myself in a very unusual situation where I want to opt to claim tax residency in both Portugal and the UK, while there is a double-taxation treaty in place.
I want to stay in the UK for another year (for family reasons), but I need to get a Portuguese tax residency to obtain an NHR (non-habitual residency). The latter scheme is expiring in the next few months.
If the two did not have a double-taxation treaty, I think this would be relatively straightforward and I could just pay taxes in both countries as one normally would. However, under the treaty, I would definitely qualify as a UK resident for the period under question.
What I would like to know is if a double-taxation treaty is a right or an obligation - i.e. can I opt to pay taxes in both countries even though I am not obligated to?