If the tribal nations are indeed states, then they would have to open diplomatic relationships with the UK to get their passports recognized. In that case, the

If the tribal nations are indeed states, then they would have to open diplomatic relationships with the UK to get their passports recognized. In that case, the USA is a third party and not responsible for their recognition. If in turn the US government manages to get the UK to accept their passport, then this would be evidence that the tribes are not sovereign regarding international law.