Thomas Cook is pursuing a claim for more than £500 million damages against the European Commission over Brussels’ veto of a proposed merger between Airtours and First Choice nine years ago.

Airtours, later renamed MyTravel, merged with Thomas Cook last year. First Choice is now part of rival TUI Travel.

The EC blocked the deal in 1999 on the grounds that it would distort the UK travel market. Airtours had the ruling overturned on appeal in 2002 and submitted a claim for damages in 2003.

The case has been lumbering through the European legal system since. But a ruling last year in a separate case for damages against an EC prohibition on a merger between two electrical companies in France appeared to open the way to what is now the Thomas Cook claim.

Lawyers for the company told the European Court of First Instance in Luxembourg: “The Commission would have been more correct if it had tossed a coin.”

The EC is appealing against the successful damages claim.