It has long cost more than a penny to use a public lavatory but Ryanair is threatening to bring a whole new meaning to sky-high prices by charging passengers to use its aircraft's toilets.

Michael O'Leary, the budget airline's chief executive, revealed today that it is considering coin slots on cubicle doors.

"One thing we have looked at in the past and are looking at again is the possibility of maybe putting a coin slot on the toilet door so that people might actually have to spend a pound to spend a penny in future," he told BBC Breakfast.

He insisted this would not inconvenience passengers. "We are always looking at ways of constantly lowering the cost of air travel and making it affordable and easier for all passengers to fly with us. I don't think there is anybody in history that has got on board a Ryanair craft with less than a pound. What do you do at Liverpool Street station at the moment [when] you need to spend a penny? I think you have to spend 20p to go to the toilets."

Ryanair recently announced it is to shut check-in desks at airports and have passengers check in online instead, and has also decided to end any prospect of peace and quiet on flights by introducing mobile phones. "Our flights are not cathedral-like sanctuaries," O'Leary said last week. Now, it seems passengers might have to cross their legs while phoning home.

The company offers low headline fares but charges extra for items such as additional baggage. Earlier this month, it confirmed it is to charge passengers £30 if they cannot pack their duty free into their single piece of hand luggage.

"We're all about finding ways of raising discretionary revenue so we can keep lowering the cost of air travel," O'Leary said. "In the last year we have reduced our fares by 10% when British Airways and others were whacking up their fares and whacking up their fuel surcharges. We guarantee the lowest fares and guarantee no fuel surcharges as well."

But consumer group Which? accused Ryanair of putting profit before the comfort of its passengers and being "prepared to plumb any depth to make a fast buck". Rochelle Turner, head of research at Which? Holiday, said: "Charging people to go to the toilet might result in fewer people buying overpriced drinks on board. That would serve Ryanair right."

Stephen McNamara from Ryanair said: "Michael makes a lot of this stuff up as he goes along and while this has been discussed internally there are no immediate plans to introduce it."

He added: "Not everyone uses the toilet on board one of our flights but those that do could help to reduce airfares for all passengers. Then again, maybe O'Leary was just taking the piss this morning."

Plane speaking – 10 chargeable things to check before you fly (airline practices and prices vary)

Check-in desk fee

Storing baggage in the hold

Speedy boarding

Storing sports and musical equipment

In-flight food and drink

Oxygen for those with medical conditions

Changing flight

Name change on a ticket

Payment handling fee

Charge to recipients of gift vouchers