Eurostar has been reprimanded by the advertising watchdog after promoting a £39 fare that applied to only a “very small percentage” of available seats.

The email of July 15 included the subject line, “Soak up every second of summer,” and went on to read: “Treat yourself to a European getaway … from just £39 each way.”

Further text stated: “Make the most of the long days and sunny rays with a summer getaway in August or September. Book now to grab a bargain to Paris, Brussels or Lille.”

The complainant, who was only able to find one ticket from London to Paris at the advertised price, challenged whether the ad was misleading.

Eurostar said that a total of 39,000 seats had been available at the advertised “from” price across the routes, which they believed was a significant number and gave consumers a reasonable chance of obtaining the lowest advertised fare.

The firm said they did not know when the complainant searched for a ticket but that from July 12 onwards the number of available tickets at the stated price for travel to Paris in August and September would have decreased as they were sold.

The Advertising Standards Authority (ASA) said consumers would understand the ad to mean that a significant proportion of fares to the advertised locations of Paris, Brussels or Lille would be available to buy at £39 throughout August and September, and that they would expect to find the tickets available at the “from” price across a range of dates and times within that period and have a reasonable chance of obtaining them.

It found that as of July 12, there had been 9,500 standard class seats available on both the outward and return journey at the stated “from” price for travel between August 16 and December 13.

The ASA said that data provided by Eurostar showed that the £39 fares “had made up a very small percentage of available tickets for travel between London and Paris, and Paris and London”.

The watchdog said: “We therefore considered that Eurostar had not demonstrated that a significant proportion of tickets between London to Paris and Paris to London had been available ‘from’ £39 during the promotional period.”

It also found that as of July 12 there had been 6,500 seats available from London to Brussels and Lille, and 13,500 seats available from Brussels and Lille to London – again a “very small percentage of the total number of seats available for standard class travel for those routes in the identified timeframe”.

“We therefore considered that Eurostar had also not demonstrated that a significant proportion of tickets for the London to Brussels and Lille routes had been available ‘from’ £39 during the promotional period,” the ASA concluded.

It said: “We acknowledged that the terms and conditions of the promotion had stated the number of seats available, and that they were subject to availability.

“However, because we considered that a significant proportion of tickets had not been available at the ‘from’ price, we concluded that the claim ‘Treat yourself to a European getaway from just £39 each way … with a summer getaway in August or September’ was therefore misleading.”

The ASA told Eurostar to ensure that when using “from” price claims in future, a significant proportion of the fares were available at the advertised price.

A Eurostar spokeswoman said: “We value customer feedback, including complaints, and take great care in the way that we word our advertising and the number of tickets that we offer at the promotional price during particular time periods.

“We understand and take on board the ASA’s ruling which is related to seat availability in part of the promotional period, and we are committed to ensuring that this scenario does not occur again.”