I'm heading to Belfast this summer, so I purchased a BM mini-griptilian to replace my TSEK. Then I found out that a locking blade is considered "not a pocket knife". Then I found out that unless you are currently using a knife for a legitimate purpose its not necessarily legal to possess one...

Also found out that having a knife (any knife) in your car can be considered "on your person" even if you are not in, or even relatively near your car (I believe that was how it was explained).
The advice I garnered from my inquiries was this...
If you are a tourist, you can probably get away with a Swiss Army Knife under most situations, with discrete carry, and sane behaviour, but not necessarily. Ensure that maximum length of any blade (I dunno about a saw blade..) is < 3". If you look suspicious, are a prick, or generally give a LEO any indication that you are not apologetic and appalled at yourself for your ignorance of their knife laws, you could be in for confiscation, or some serious complications.
No locking blades in the UK (dunno how this relates to the Republic), apparently there was a ruling that indicated a locking folder is considered a fixed blade, and not a pocket knife...This INCLUDES multi tools. So no leatherman WAVE (though I will be bringing my Leatherman Juice in lieu of my mini-grip, small, colourful, and no locking blades)
Don't even imagine/dream/fantasize about bringing ANY blade into a pub or other establishment that serves alcohol. Think twice about nail clippers. When your pints come in plastic glasses, you'll realize just how preventative some establishments can be of escalated violence... there is no valid explanation for carrying a blade in a bar/pub/whatever, and you'll be a long long way from home trying to explain that "where you're from it's perfectly normal...". Also, Spyderco's are some of the meanest looking knives out there, esp. to sheeple. Doubly so if its a spyderedge. I don't mean to sound preachy, but it's my understanding that knives are even more feared by the general public "over there", than "over here". A SAK might be considered a tool. Nearly anything else is considered a "knife!".
Regards,
Shaun.