EasyJet has been told to stop claiming that carry-on baggage fees are available “from £5.99”, after it failed to provide evidence to the advertising watchdog that passengers can stow luggage in a cabin at that price.

The Advertising Standards Authority (ASA) said customers would assume from EasyJet’s wording they could take their bags on flights for £5.99.

The claim on EasyJet’s website was flagged to the ASA by consumer group Which?, which said airlines often advertise low fares but have additional fees.

EasyJet said: “We always aim to provide clear information to our customers on pricing and the purpose of this page was to display factual information on fees and charges to customers.

“We always have some large cabin bags available for the lowest price. In light of the ASA’s feedback we have made some changes to the page to ensure the information is as clear as possible for consumers.

It said the wording on the website was meant to inform customers that £5.99 was the starting point for adding carry-on bags and it was an accurate price on several routes.

The airline said the fact there were no bags available for less than that price meant the claim was not misleading.

Responding to the complaint from Which?, the ASA said it expected to see evidence that large cabin bags could be booked for £5.99 but EasyJet did not provide this.

It said consumers would take the “from £5.99” claim to mean that large cabin bags would be available for that price “across a significant proportion of flight routes and dates”.

As a result, the watchdog ruled the claim was misleading and told EasyJet not to use that wording in future.

EasyJet informed the ASA that the section of its website where this claim appeared was intended for information purposes, not marketing or promotion.

The airline’s website now states: “Fees vary with demand, route, flight date and time of booking. You’ll see exact price at time of purchase.”

The airline said it was “not able to provide specific figures” because cabin bag prices depend on a number of factors including availability and demand.

It said that customers would clearly see the actual price of a cabin bag when they were booking a flight.

Which? said its own research showed that typical cabin bag prices for EasyJet were five times as high as the £5.99 claim.

Rory Boland, editor of Which? Travel said that there is a “culture” of airlines using “low headline fares, then charging exorbitant prices on top to take a standard cabin bag”.

“It’s frankly astonishing that airlines think they can ignore the rules and mislead customers with unattainable prices, so it’s absolutely right that the ASA has made this ruling,” he said.

“When booking a trip, customers should consider choosing an airline without cabin bag add-ons as it may work out cheaper.”

Jayne Hawkes, a consumer rights expert, said the issue was not unique to EasyJet.

“It only serves to reduce customer confidence [if airlines] increase confusion about baggage,” she told the BBC.

Last year, European Union lawmakers voted to force airlines to let passengers bring a carry-on bag of up to 7kgs on board for free.

The law has not yet been implemented as it has to be approved by member states.