Cabbage - now that wouldn't be a bad idea. A very significant plant in Irish cuisine, second only to the potato. And with no sectarian overtones thta I have ever hear of. And no more absurd than the Welsh having the leek as a national symbol.
There are national animals and national flowers - how about a national vegetable? Nominations invited.
Here is a bit more about the St Patrick's Day events in Trafalgar Sqaure and so forth.
Now would this be a good occasion for people to test out the Public Entertainment Licence state of play in London? Would they really bring the law down on people who wished to make music in public places on that day without a PEL being in place?