You should find out exactly how much it is to break the fixed rate and crunch the numbers. You need to also calculate the blend of the 3% and the "commercial rate" for the amount you want. For e.g. if the "commercial rate" is 6%, then your blended rate is 4%, which is pretty good. Do you have a HR dept that can talk you through this? Presume the 3% is part of an employee benefit package so they should be able to tell you exactly what your repayments are.
First thing you need to do is find out what your penalty is for breaking the fixed rate mortgage. Then find out how long the 3% lasts (e.g. will that go up at any stage? Do you lose this rate if you leave the bank?) You also have to factor in legal costs for switching but if you can get an overall rate of 4% for the entire mortgage, then that's a really good rate.
Sprite