European anti-monopoly authorities today launched a probe into British Airways' planned tie-up with American Airlines and Spanish carrier Iberia.

Virgin boss Sir Richard Branson has condemned the deal as creating a "monster monopoly".

A European Commission spokesman said: "We have opened, on our own initiative, an investigation under the treaty's anti-trust rules."

BA stressed it had expected such an investigation. A spokeswoman said: "This is a normal part of the process - nothing to surprise us at all."

However, Virgin Atlantic chief executive Steve Ridgway said: "The EC has rightly begun an investigation because they understand that consumers will be worse off if this alliance proceeds."

Virgin claims the tie-up would give the trio control over nearly half of Heathrow's take-off and landing slots and 63% to 80% of all flights between Heathrow and key US airports such as New York's JFK and Chicago.

BA and its proposed partners announced their tie-up this month as a result of the new US-European "open skies" agreement. Such alliances allow airlines to share routes, meaning fewer empty seats on duplicate flights. Virgin argues it leads to higher prices but BA says the move will provide easier, seamless travel and cost savings that can be used to keep down fares.