The ASA said the lowest amount payable was �11.70

The Irish carrier's fare failed to include non-optional extra taxes and charges, the Advertising Standards Authority (ASA) said.

These extra costs were anything from �11.70 to �21.70 across 20 UK airports.

But Ryanair, which is seeking to take over Irish rival Aer Lingus, said more than 14 million people viewed the ad and not one passenger had complained.

The advert's voice-over said Ryanair had "released four million zero fare seats on its website in an amazing autumn sale".

It added: "All fares under this offer are zero. Only taxes and charges are payable and we guarantee no fuel surcharges."

And large on-screen text said: "4 million seats �0 fare".

Previous rulings

After an investigation, prompted by a complaint from Monarch Airlines, the ASA found Ryanair in breach of advertising rules relating to pricing requirements.

It said the lowest amount payable was �11.70, and fares should have been advertising as starting at that price.

The ASA has ordered Ryanair not to repeat the advertisement.

Broadcaster ITV said viewers would have realised that flight costs would include taxes and charges on top of the �0 fee.

In May this year, the ASA upheld a complaint against Ryanair about an advert for three million free tickets.

It said the promotion failed to make clear that the offer did not include flights on Fridays.

Two years ago the ASA criticised Ryanair for a promotion for "giveaway" flights because passengers would have to pay charges and taxes.