Hello????? The "£5 surcharge" is presumably a passenger handling charge - even if it is an increased one. That's what airports charge for handling airlines ... which is how they make their money ... which is how they stay in business, build terminals, pay for their own staff and so on.
It's probably not dissimilar to what all airlines at LHR had to pay to fund Terminal 5 (despite the fact that the usual way of funding business development is for the business to take the risk, rather than their customers). And what airlines at LHR, STN and LGW will have to pay to fund the new runway at STN when the time comes.
No, come to think of it, it's not like that. It is a legitimate charge. NQY doubtless had to think hard before putting it forward, because whenever a business increases charges, it runs the risk of losing its customers - especially ones like Ryanair who keep costs down by getting people to pay them to come. But it is reasonable to propose an increase - that's what businesses have to do sometimes.