Under U.K. law citizens of the Republic of Ireland can legally travel back and forth across the Irish sea without a passport. So Guido is legally able to enter the country and do what he can to assist in the overthrow of the government, without being legally required to carry identification. Unlike British subjects, Guido is free to travel in and out of the U.K. without a passport or a UK I.D. card – and the English call the Irish thick!
Whilst on the subject, let me recommend the benefits of Free Ireland to you over-taxed and downtrodden subjects: lower taxes, higher per capita income, higher GDP growth, a fully functioning education system, no I.D. cards, no kow-towing to inbred-German-toffs, a friendlier people and a better lifestyle.