Passengers who consistently refuse to pay the controversial airport tax at Norwich International are put on a blacklist and could be banned from flying from there in future, it emerged last night.

Passengers who consistently refuse to pay the controversial airport tax at Norwich International are put on a blacklist and could be banned from flying from there in future, it emerged last night.

The £3 airport development fee (ADF) - aimed at generating £18m to improve the airport - has come in for criticism from the airport's main flight operator, Flybe, since it was introduced in April.

Holidaymakers have shown a mixed response, with some angered at having to pay extra and others believing the overall cost is still cheaper than flying from a London airport.

Now it has emerged that while passengers who refuse to pay the fee at check-in are allowed on their flight in the first instance, those who continue to refuse to pay will be placed on a database and could be prevented from boarding in future.

And the possibility that the charge might even be illegal was raised by consumer watchdog Which? last night.

Asked by the EDP to look into the refusal to allow passengers to board, spokesman Rebecca Leach said: “I have spoken to the legal team and we cannot say if this charge is illegal. We do not have enough background information to take a stance either way, and this is quite a grey area.”

A letter signed by Norwich International's managing director, Richard Jenner, is sent to each non-payer warning they should pay next time they fly or “not book flights from Norwich International”.

“On this occasion you were allowed to travel because you may not have been aware of the ADF when you booked your flight,” the letter states.

“However, please note that if you travel from Norwich International Airport in future, you will be expected to pay the ADF.

“If you again refuse to pay the fee, your name will be placed on a database and we reserve the right to deny boarding on your flight.”

It continues: “I very much hope you will continue to use Norwich International Airport. The vast majority of our passengers are content to pay the ADF, which is used to improve facilities at the airport.

“However, unless you are prepared to pay the fee I would ask you not to book flights from Norwich International”.

Airport spokesman Louise Wilkinson said the names of 105 customers who have consistently refused to pay the ADF are on a database, which represents 0.02pc of the half a million passengers who had travelled through Norwich International since April.

She said names placed on the list were for staff to check and not for public consumption, and refusing a passenger access to the departure lounge would be “an absolute last resort”.

“We would hope to come to some kind of solution before that happened,” she said.

In July Flybe claimed it was forced to withdraw flights to Malaga and Alicante from the airport's winter timetable because the fee had had a “profound effect on ticket sales”. The airport strongly refuted this and said Flybe was struggling against its low-cost competitors.

A Flybe spokesman said: “Flybe have been opposed to the development fee from the start. It acts as a barrier to passengers who might think of flying from Norwich and Flybe would not countenance any move to prevent passengers from flying on our aircraft.”

Darren Roberts, communications manager at Eastern Airways which runs flights between Norwich and Scotland, said: “Norwich airport has imposed this charge and deliberately chosen to levy it against the passenger rather than the airline.

“Eastern Airways highlights the existence of the airport's passenger levy on its website. What the airport does is out of its control.”

A reference to the ADF is on the home page of the Norwich International website, along with a question and answer section. It states the “the airport reserves the right to refuse to handle any passenger unless he/she has paid the fee”.

Passengers booking online with Flybe are also warned about the extra charge at Norwich check-in before they have paid for their tickets.