Ryanair's service from Stansted to Frankfurt, which starts on 22 April, lands at Hahn - a former United States air force base 75 miles from the city. Passengers will then have to take a 75-minute coach ride to Frankfurt or hail a taxi to the nearest railway station 25 miles away for a connecting train.
Ryanair has been repeatedly condemned for similar services. Three complaints have already been upheld by the Advertising Standards Authority.
The ASA confirmed yesterday it was likely to investigate the latest service. It has already received a telephone complaint and will act once it has written confirmation. "Ryanair are responsible for most of the problems in the flight industry on misnaming of airports," ASA spokesman Steve Ballinger said.
The previously upheld complaints relate to Ryanair listing Venice as a destination for flights that land at Treviso 15 miles away, flights advertised for Oslo that landed 50 miles away at Torp airport, and a Stockholm service that flew to Skavsta, 80 miles away.
Ryanair's marketing director, Tim Jeans, defended the advertisement for the latest service. He said that passengers would be told the airport details before they confirmed their booking. Although Stockholm, Oslo, Frankfurt and Venice all have nearer airports, they are designated by the International Air Transport Association as city airports, he said.
He added: "We have taken issue with ASA because we believe we are being discriminated against because those airports are officially designated as airports for that city."
He said the lower costs of operating from little-used small airports allowed Ryanair to offer a fare of pounds 69.99 to Hahn - a fraction of the price charged by the major carriers. Hahn is likely to become an increasingly popular destination as Frankfurt airport is officially full up, Mr Jeans added.
But Mr Ballinger said: "We think it is for the ASA to interpret the advert and not the advertiser, who has a vested interest."
The issue highlights the growth in popularity of small airports, which are cheaper and less congested than their bigger rivals. Many European cities, including Paris, Dusseldorf, Rome and Milan, have secondary airports.
Deregulation has allowed smaller operators to break monopolies held by the European state airlines but high charges at the traditional airports forced them to look elsewhere. Congestion at the London airports Heathrow and Gatwick prompted budget airlines such as British Airways' Go, Ryanair, Debonair and easyJet to use Stansted or Luton. Other secondary airports include Prestwick, 30 miles from Glasgow, and Liverpool, 30 miles from the major airport at Manchester.
Debonair, which flies from Luton to Paris Pontoise, 22 miles north of the city, claimed it took only 30 minutes by train to reach the centre and was a more pleasant experience than passing through Charles de Gaulle.
EasyJet, which uses Luton and Liverpool, said it could offer cheaper fares because it saved on landing and handling charges, and because aircraft could be turned around more quickly. The company's spokesman, James Rothnie, said: "We can have a Luton-based Boeing 737 flying for 12 hours, while at Heathrow it would fly for seven hours, because of the fast turnaround times between landing and take-off."
t The International Fund for Animal Welfare (IFAW) has been criticised by the Advertising Standards Authority over claims in an anti-foxhunting advertisement. The authority upheld three complaints by the Countryside Alliance, the Cattistock Hunt and members of the public about the advertisement, which appeared in the national press and showed a photograph of a pack of hounds ripping a fox apart under the headline "RIP".
The ASA said in its monthly report that IFAW's accompanying claim that "one [fox] that died this way was found with lungs full of soil" was "an exaggeration" that did not have enough evidence to support it. It asked that in future such claims should not be repeated unless they had full supporting evidence.