Megabus has been banned from advertising fares "from £1*" after the Advertising Standards Authority said consumers should reasonably be able to expect to find seats at that price.
The company admitted that only one seat per coach is available at that price on some journeys.
Megabus's advertising strategy had previously focused on the lowest available prices, with a recent Aberystwyth to Birmingham route carrying the "from £1" tag and a Facebook post promising "day trips from £1" from London to Bath.
In fact, only 4 per cent of the Aberystwyth-Birmingham seats were available so cheaply, with the London-Bath route faring worse at 3 per cent - and some of those tickets were for stops along the route.
Only one ticket
One of the ads cited by the ASA (Photo: PA)
"We considered that those figures did not represent a significant proportion of seats being available at the advertised 'from' price for those routes," the ASA said.
"We noted in particular that only one of the £1 fares on the London to Bath route was for the full length of the route."
Most customers will not have been able to find £1 trips when attempting to book in advance, the ASA decided.
Megabus, which is operated by Stagecoach, a company that has run many city bus services as well as the contested Virgin East Coast mainline, said £1 were generally available if booked far enough in advance depending on route.
However, a spokeswoman said the company would no longer focus specifically on price in future advertising.
A Megabus spokeswoman said: "We have always provided clear and transparent pricing for all of our customers, including the many thousands who have taken advantage of our great £1 seat offer.
"While we will continue to offer seats from £1, in line with recommendations from the ASA, we have decided to focus our marketing on the great value that all megabus.com fares offer, along with welcome extras such as on board wi-fi and charging points."
This piece originally appeared on our sister site iNews