Non EU players need a work permit in the UK. Per 2105 the requirements have been amended.
The basic idea is that a player shouldbe of a such a high level that a similar player can not be found in the UK itself. In order to determine that a player has such level the authoritities reuire that a player has played a certain amount of matches for his national team and that the national team needs to be of a certain quality. The latter determined by the ranking of the national team. The lower the ranking the more matches a player is required to have played.
Herunder the summery of the sytem as published on the fa's website.
New work permit system per 2015:
Required % of international matches over previous 24 months is determined by the player’s National Association’s official FIFA ranking:
FIFA 1-10: 30% and above
FIFA 11-20: 45% and above
FIFA 21-30: 60% and above
FIFA 31-50: 75% and above
Reference period reduced to 12 months for those players aged 21 or under at time of application