For risk averse me, I always try and fix 5 years at a time.
It's essentially a gamble on what interest rates will be like in 2 years' time. Still low and you've "wasted" £2400. If they've rocketed up then you could be saving quite a bit more than that over the subsequent 3 years.
Looks like the online application for Halifax is fairly straight forward.
I'm on a 4.79% deal fixed for 2 years until end Sept 2017
Tentative check shows me that I could likely (if I was looking to switch now) get either;
a 2 year fixed at 2.89% - saving me £250 a month
a 5 year fixed at 3.98% - saving me £150 a month
Hypothetically, which of those sounds more appealing?