Hi Kieran,
I'm in roughly the same position as you - at the end of my second fixed term with Ulster Bank. I was originally on a flexible rate which tracked the ECB rate + 0.95%.
Ulster Bank have asked me to send in original documentation - the documentation doesn't actually say that I should be given the option to revert back to the original rate - I'm just wondering did your docs specify that?
As regards your question, I suspect you could go after them, whether you want to is another thing.
To be honest I'd be very happy to get back on my tracker!
Cheers - Maggs.