The United Kingdom is a state, not a country.
Scotland, England, NI and Wales remain therefore countries.
They are countries that are a part of a larger state.
The football team argument therefore is a non-starter. Irrelevant.
Watching Scotland’s friendly with the US last night, the commentators discussed the problems with the “British” team that was to be fielded for the 2012 Olympics. The soccer organizations of Scotland & Wales told their players not to participate, as they felt it would jeopardize their independence in terms of FIFA. They fear that FIFA (which has more members than the UN) would consider them part of the larger country (and make them play as part of one).
A very valid concern; you’ll never convince countries that are at war with Britain that they’re individual countries.