To answer you Sarenco, there were different types of fixed rates. For example if a person took a new mortgage fixed for say the first 2 yrs then the loan offer would say under the rate part the fixed rate and what type of rate thereafter, be it tracker or variable. For a period while trackers were everywhere practically all mortgages issued on this basis would have been reverting to tracker. These mortgage holders would get a letter a month or so before their fixed rate was up giving them the options of whatever new fixed rates were there, if they did not tick a box for a new fixed rate the loan would automatically on maturity go back to whatever rate was specified in their original loan offer. When this was a tracker they would get ECB plus whatever margin their loan offer stated. There was not a box to tick on the letter to go to tracker because that would automatically happen if you didn't want a further fixed rate, it wasn't an option as such, the loan was a tracker. I can't recall the exact wording of the letter, I don't think it would have spelled out what actual rate you returned to if a tracker as there were many different margins a person could be on, any reference to what would happen if you didn't pick a fixed was more likely to just refer to the rate specified on your loan offer. Any loan offer that said fixed for x time & thereafter ECB+ whatever should automatically go back to tracker when the fixed matured. I regularly called people re the letters and explained that if they wanted to go back to tracker (which to most people just meant variable) then they were to do nothing, no need to return the letter with the fixed options.
It was different where someone chose to switch to a fixed rate where they may have had a variable mortgage for some years, they would sign a fixed rate appendix to switch and when the fixed ended they would go back to whatever they came from, if that was a variable rather than a tracker they would return to the variable rate being offered at that time. There would be no mentions of trackers in their case unless it was during one of the many campaigns to get customers to switch to them, in that case they might turn up on my list to contact. If they did switch to tracker and then subsequently fix they had no automatic right to go back to a tracker if they were no longer being issued at the time of maturity of the fixed rate, if they were still there they could have one, if they were gone the original loan offer dictated rate.
Again it never happened while I worked there that we in the branch actively tried to get people off trackers, some posters clearly don't believe me, I don't care. Yes indeed I was only one of the plebs outside of Head Office but I was the mortgage advisor in my branch and responsible for the branches lending, I can honestly say I never advised anyone of something I did not think was in their best interest, now hindsight is marvellous and if I made mistakes it was with the right intentions (buying bank shares myself was one I was guilty of

) I knew many of the head office lending staff and would be in contact practically daily but while we often discussed the bad lending being done and the lax guidelines, trackers were never a hot item at that time.
However I definitely believe at some stage after 2010 there was something done to the default on these loans as too many people did not automatically revert, there is a very interesting thread on Rollercoaster by Lucybousy with lots of case, I think she also posted here about her case.