BOI's one year fixed rate for LTVs over 80% is 3.65%.
Is it possible that BOI's SVR will fall below 3.65% in the next 12 months? Yes, it's certainly possible but it doesn't look very likely at the moment.
Is it possible that BOI's SVR will fall quickly enough and far enough that you would be better off not taking the 1 year today? Again, it's possible but that looks even more unlikely.
Even if BOI's SVR fell from 4.5% to, say, 3% in six months' time, you would still come out well ahead after 12 months if you fixed @3.65% today.
If you can't switch, it makes sense to take the 1 year fix.