Some other observations...
As attested to by posters on other threads switching is a painful process and inevitably takes much longer than you would expect at the outset - valuations, bank meetings, loan approvals, redemption letters, queries to banks and solicitors and the gaps between each all add up. Being realistic 6 months plus is what you are looking at. It's all well and good saying it shouldn't take that long, but it will. For a 0.1% or 0.2% saving in my view the hassle probably isn't worth it. There are costs too (legal fees, valuation, your time) though many banks offer switchers cash toward legal fees and/or free valuations.
As Fita also discovered BOI will drop their SVR for existing customers, if you ask, especially if you credibly look like you're about to switch. Even still though they won't match competitor banks on SVRs. But its an easy way to try seek some reduction without the hassle of switching, if it doesn't suit you go through that process right now. Given my own experience and reading other threads on AAM I'd say up to about 0.3-0.5% under advertised BOI rates seems to be on the table. Presumably people's mileage will vary, depending on how credible your switch threat is, and lower LTVs will probably get a better hearing, but it's worth a try.
Good luck to anyone looking to switch.