UB - new fixed rates as low as 3.3%

[Generic Name]

Actually, I just rang KBC saying I was a new customer with 60% LTV and asked them what would happen after a year.

Like you said (Generic Name) after a year they won't go to "Existing Customer" rates. You'll still be classed on your LTV and you'll still have the cheaper rates.
So I'm definitely moving off KBC now. I'm on close to 60% and they're charging me 4.3%.

If you go to them with a viable alternative, e.g. the BOI 2% cash back offer or whatever other offers that may arise in the coming weeks/months, then they may do something for you to keep the business. At near 60% LTV your in a strong position. I'm with them also and that's my plan. Just waiting to see what other offers come along. Best of luck with it.