Hi Glenn
It depends on the wording of your loan offer/mortgage contract.
Some say "Your margin is 1% over ECB and will be so for the term of the mortgage".
If ptsb makes it clear in their fixed rate agreement that you are giving up your tracker, it would be hard to persuade them to give it back.
Some other contracts say "At the end of the fixed rate period, you will be offered a tracker at the then current rates" - this is worth nothing as the then current margin will probably be 3%.
Get a copy of your mortgage contract from your solicitor or from the lender if you don't have it yourself.
Brendan