I really don't see why you have to tell the bank that you are renting out your ppr - their interest is in ensuring you pay the mortgage in full and on time. We changed to a tracker mortgage in 2007 on our PPR while it was being rented out (we were living abroad). Its still your family home and. from what I recall, we just told the bank that it was our PPR and was being temporarily rented out and they were happy to give us a PPR mortgage. Now obviously times have changed and the banks are more cautious but I still can't see that you are legally liable to tell the bank as long as you have no issues with paying the mortgage.
If you think about it, lots of people, especially on trackers, got their mortgage rate over the past few years on the basis of a specific LTV ratio (including us). Those LTVs have all changed, so theoretically the terms under which we were lent the money have changed, but I am not planning on calling the bank any time soon to let them know that our LTV no longer complies with the conditions of the mortgage and I haven't heard of anyone else doing so either! Your circumstances have also changed since you took out the mortgage but I don't see why you have any more obligation than I do to inform the bank.
Of course, as you said, you need to inform Revenue immediately and get the TRS cancelled and declare all the income for tax purposes.