Yes I have fixed recently from an SVR of 4.3% on an apartment I bought in 2006, so lots of negative equity and I can't switch.
There are lots of rates if you have good LTV, look at their website. What is not clear though is if you have a crappy LTV of over 100% (they say over 90% on the forms), you can still fix for 3 years at 3.65%, which saved me over €100 per month. I was not asked for proof but I recall the offer letter did mention you would have to use an official valuer of taking a better option.
I do expect SVRs for good LTVs to keep falling, but since the banks can continue to screw negative equity mortgage holders with SVRs with impunity, I don't expect to get a better deal than from UB anytime soon.