Photography on London Underground is allowed (once you dont use flash). Just carry a camera on Irish public trasport and you'll be hopped on by some idiotic security guard. I did a little googling and found the exact phrasing of the railway bye-laws in Ireland...
LIGHT RAILWAY (REGULATION OF TRAVEL AND USE) BYE-LAWS 2004STATUTORY INSTRUMENTS S.I. No. 100 of 2004
6 (1) A person shall not on a light rail vehicle or a light railway without permission given by or on behalf of an operator -
(f) use any camera or video recorder or any form of equipment for recording sound or images so as to interfere with any other person
"SO AS TO INTERFERE WITH ANY OTHER PERSON" So is photography actually allowed on trans and darts in Ireland?