Both are nationalities and with it are protected characteristics under the Crime and Disorder Act 1998.
That Act deals with racial and religious offences. Miscreants are usually landed with a racially or religiously aggravated public order charge. As the examples below demonstrate, remarks most would consider far less insulting than what's often hurled from football stands are prosecuted.
Woman fined for 'racist' English insult -
A Welsh woman has been made to pay compensation for using a racist slur against an English woman after calling her "an English cow".
More: https://www.telegraph.co.uk/news/ukn...sh-insult.html
Man fined for racism after calling Welsh people 'sheep s******s - https://www.independent.co.uk/news/u...s-8594480.html
Councillor fined £750 for calling Welshman 'boyo' - https://www.independent.co.uk/news/u...o-8689295.html