I'm not sure whether the d_mcevoy has serious grounds for complaint but in any case, here's some background to give some perspective on these fees in case anyone is interested. Whether d_mcevoy was ill advised is a different issue.
The quoted 19k is correctly called a breakage fee and not a fine or administration fee. You may think that the bank could just be nice and "waive" this fee but this fee represents a real cost for the bank and not some capricious way of punishing customers who "bet" incorrectly on interest rate movements.
Breakage fees work pretty much the same whether for a loan or for fixed rate savings (for example term deposit savings).
In the case of "switching to variable rate", it's the same as you canceling your original loan and taking out a new one as far as the bank is concerned. Even if you weren't to re-mortgage but just turned up with a suitcase full of cash to pay off your mortgage, you would be charged a breakage fee.
When you borrow from a bank on a fixed rate the bank effectively borrows the money in the markets at the prevailing rates (actually this isn't fully accurate, the bank's treasury department generally handles this) for the term. The point is that the bank has locked itself into a repayment schedule.
So say a customer borrows 500k at 5% fixed for 5 years. The bank (effectively) borrows the money in the markets - lets say at 3.5% for 5 years. Normally this guarantees profit for the bank (they collect 5% interest but pay 3.5%) but the problem is that the bank is effectively locked into this loan while the customer generally has some sort of option to break the term of their loan.
If the customer wants to "break" the term of the loan - let's say 2 years in - then the bank still has to make the payments on the loan it has taken out from the markets. So the bank effectively takes the returned loan money and lends it in the markets at a fixed rate for the remainder of the term and uses the interest it makes to make the payments on it's original money market loan.
If the interest it makes with this investment in the money markets is less than that required to service its first loan (e.g. in this case, if three year interest rates are less than what 5 year rates were 2 years ago), then there is a shortfall for the bank. This shortfall is recovered from the customer in the form of a breakage fee.
Having said that, if the converse holds (e.g. in this case, if three year interest rates are GREATER THAN what 5 year rates were 2 years ago) the bank will make extra money if you redeem early but I don't know of any bank who offer a "breakage" bonus.