Ryanair has been banned from claiming its flight from London to Brussels is faster and cheaper than making the journey by Eurostar.
It is not the first time that Ryanair has been reprimanded by the ASA
The claim was misleading because it ignored time taken travelling from city centres to airports, the Advertising Standards Authority (ASA) said.
Ryanair's advert compared its 70-minute flight with a 131-minute train journey.
But travelling from the heart of London and Brussels would add one hour and 45 minutes to the journey, the ASA said.
And costs for those journeys to and from airports at both ends of the journey meant that claims Ryanair's service was cheaper were also misleading.
Ryanair defended its position, saying that time and costs involved in getting to an airport or railway station were "irrelevant" as they applied to both modes of transport.
In a statement, the airline added that "no stupid ruling" from the ASA could hide the success of the airline.
"Only the very rich or the very slow waste their time on Eurostar," it said.
Ryanair's main London base, Stansted airport, is about 25 miles outside the centre of the capital while Charleroi airport is some 28.5 miles outside of Brussels.
"We considered that many readers would not be aware of the locations of the airports and additional costs incurred," the ASA said.
Ryanair was also found to have made inaccurate claims when it said that Ryanair's flights on the route were more punctual than Eurostar's service.
The budget airline was told by the ASA to remove all the claims from its adverts.
In July the ASA ordered Ryanair not to repeat an advertisement that played down the impact of aviation on the environment.
In a press campaign the airline claimed the airline industry "accounts for just 2% of carbon dioxide emissions".
The ASA ruled it breached rules on truthfulness by not explaining the figure was based on global rather than UK emissions.