Marks and Spencer has lost a five-year legal battle with Interflora after it bought advertising space tied to Google searches for the flower delivery network's name.

Mr Justice Arnold at the high court in London ruled that M&S's use of the Interflora trademark to advertise its flowers and gifts range was trademark infringement.

He said the M&S adverts did not enable "reasonably well-informed and reasonably attentive" internet users to work out whether the company was part of the Interflora network.

Rhys Hughes, president of Interflora's British unit, welcomed the decision. He said: "Keyword advertising is a very powerful tool and so it is vital for consumer protection that internet search results take consumers directly to the brands they are looking for."

On Tuesday a search for Interflora on Google still displayed M&S Flowers, the retailer's next day delivery service, in the yellow advertising box on the site.

M&S can appeal against the high court decision and a further hearing will decide the level of damages M&S will have to pay. A spokeswoman for M&S said: "We are disappointed by today's judgement [and] are considering our position and all the options available to us."

The ruling could lead to more cases brought by businesses where rivals' adverts appear above their own links on Google's search engine.