http://news.bbc.co.uk/sport1/hi/football/internationals/7107978.stm

The problem is with this idea (cap on foreign players within the Premiership) is that it’s the “English” premiership and therefore would make no difference to Worthington’s Northern Ireland team as they are effectively foreigners as far as the English Football Association is concerned. The other home nations all have their own associations & leagues and are for the most part entirely separate entities.