Obviously you've not checked out their T&C, they say they can. I have & it says in here >> JET2 T&C ...
4.2 Taxes, fees and charges
Any taxes, fees and charges imposed by government or other authority, or by the operator of an airport and in effect on the date of travel, whether imposed directly on the passenger or payable by us on the passenger's behalf or in respect of the passenger's carriage, shall be payable by the passenger and are included in all published fare costs. A fuel supplement may also apply, in which case the full cost of the booking will be shown inclusive of this charge before you complete the booking. The taxes, fees and charges imposed on air travel are constantly changing and can be imposed after the date of issue of your itinerary/receipt. If there is any subsequent increase in a tax, fee or charge, you will be obliged to pay it. Likewise, if a new tax, fee or charge is imposed even after the date of issue or your itinerary/receipt, you will be obliged to pay it prior to departure. We reserve the right to require payment of the additional tax or charge applicable to your booking and to recover these by using the payment card advised at the time of making the flight booking. We will make reasonable efforts to contact you in advance to advise you of the payment due and approximate timescale for the deduction.
Conversely, if there is any reduction in tax, fee or charges levied and effective before the date of travel, we shall, on written request, refund you the full amount of that reduction in tax, fee or charges.