Sandman 96, if you continue S from Colombo you pass through Antarctica (and the S Pole), which, under the Antarctic convention doesn't belong to any country, and continue N up the 100th line of longitude West (approximately) and the next country you hit is Mexico. The same logic as was applied to finding Russia N of London.
Yeah, it's very close. It looks like if you measure from Big Ben you will indeed hit Ireland. But if you were to measure from, say, Croydon, you could bypass Ireland and hit Canada.
Great Quiz!!! It challenges you to take the world view on a 2D map and convert it to 3D sphere. I was questioning the Colombo to Mexico until I "folded" my 2D map and saw the answer.