For a generation large swathes of Irish men went to England and they were perceived, rightly or wrongly, as Paddy the Navvy or Mick the Bomber. When someone has a strong Irish accent they may come across as naive, uninformed and unintelligent rather the shrewd people that they often are. This combined with rampant alcohol abuse has helped create a stereotype of an Irish person in Britain.
Nowadays, Irish political and current affairs serve to perpetuate that stereotype. One viewing of the RTE Nine O'Clock news is viewed as parody by many in England. From the amateurish production of the programme to the personal appearance of the politicians ( minister for health & former minister for defence) not to mention the endemic political corruption, handling of sexual abuse by priests, grotesquely inflated public sector pay & social welfare rates. I often cringe when I think of English people tuning in.
Having had personal experience of the English approach to someone from Ireland, the initial ' friendly' response is a wistful look and some reference to alcohol consumption / abuse, which I find irritating and ( largely unintentionally) pejorative.
Collectively, I have found that Ireland is viewed as a bit of a joke really - a mickey-mouse country where you go for a break from real life hence the proliferation of Irish jokes.