w.r.t the UB offer, I think it's worth noting that nobody in their right mind will stick with a 4.5% rate after the 5 year fix unless their high LTV gives them no alternative.
In my case I'd be trading up to a house where I'd have ~40% LTV immediately, using savings I've accumulated over the last ten years of being on a cheap tracker, and the LTV would be even lower in 5 years time. That LTV will currently get me a rate of 3.85% with KBC, compared to the 3.6% 5 year fix with UB.
So it's almost worth switching to another lender immediately to save doing it in 5 years time.
Maybe that's what UB want - losing tracker customers would presumably do wonders for their net margins, arrears cases notwithstanding.