The character he played was an Irish Traveller. In the UK they are called by many names including Gypsies. In Ireland Gypsy refers to the Roma peoples. The Irish Travellers are a separate ethnic group to the Roma and were created 400 years ago when people were forced off their lands. In some places like the UK there is some integration with the Roma community but in Ireland they do not marry outside their community. The Cant they speak can have a mix between Irish, English and sometimes Roma. The Roma people as an ethnic group have existed for over a thousand years.
In addition to C Master - As a German I have also to remember, that in our cultural heritage the word "Gypsi" has a negativ connotation. During the Nazi-Aera Sinti and Romani where not only suppressed but also as "Zigeuner" (German for Gypsi) deported and killed in the KZs. That has absolutely nothing to do with the romantic picture of the "Travellers" in the movie Snatch. Today in our language the word "Gypsi" has a racist connotation.