The catch is IIB are getting away from trackers!. If you can access your original loan offer with them I would. They might have a clause in it stating that they can switch to a euribor tracker more or less at their own descretion depending on the comparison between the euribor base rate and the the ECB base rate. It's worth asking them what will happen if you don't take this fixed rate. They seem to be offering fixed rates to existing clients at the mo. I hope this helps