It had promoted the market in a poster and two emails, created by Hurrell and Dawson, in a bid to generate excitement about the opening of the new station.
The poster read: "Meet me at the farmers' market. Meet me at St Pancras International".
A complaint was made that the claim "farmers' market" was misleading, because it was not believed that the market at St Pancras station met the criteria for what constitutes a farmers' market.
The Advertising Standards Authority found itself in the odd position of making a ruling on a market that has not even opened yet.
It told London & Continental Stations & Property, which ran the poster ad, that because it could not confirm whether the market would be run by farmers selling their own produce, it was misleading to use the term at the time the ads ran.
The ads were found to be in breach of the Committee of Advertising Practice Code, on the grounds of substantiation and truthfulness. LCSP and Eurostar have been told to ensure ads do not imply a market is either currently or imminently in operation by farmers selling their own produce, if they cannot prove that it is true.