BAA is facing the threat of having to sell off three of its seven UK airports amid concerns it may be operating a monopoly.
Airlines, airport groups and rivals have been giving their reactions.
VIRGIN ATLANTIC AIRWAYS
Monopolies are not good for consumers or for airlines, because there is only one player you can talk to and only one player who can invest in most of our airports in the UK.
So this is certainly very welcome, what the Competition Commission is saying... and we back all of it.
We think the ownership structure is secondary - the focus should be on strengthening the regulatory system.
That is the way to create the capacity which is most needed, especially at Heathrow.
We are very pleased that the Competition Commission has recognised what is a fundamental problem for UK airports.
But the solution is better regulation, because each one of these airports - including those in Scotland - are local monopolies and they need better regulation, not simply being sold to another highly-indebted owner.
We welcome the commission's comprehensive report into the market power of the BAA monopoly and fully endorse its findings.
Competition works - monopolies don't. BAA's monopoly control over the London airports has been highly detrimental to competition and consumers.
BAA has long ignored the needs of its airline users and the travelling public and provided inefficient, gold-plated facilities, encouraged by an ineffectual regulator, the Civil Aviation Authority.
One of the problems of having all three [Heathrow, Gatwick and Stansted] in the same ownership has been a lack of push to get additional capacity in those airports, because they have nobody to compete to drag other airlines to their facility.
There is no competition. Gatwick management is not saying, 'Let's try and drag those airlines out of Heathrow to come to Gatwick offering better facilities and better prices,' and so you just get this lethargy of development, you get one project at a time.
While T5 has been going on, really nothing else has been going on in terms of development, so I think a lot of it is to do with just getting that additional capacity into the marketplace.
MANCHESTER AIRPORTS GROUP (MAG)
We believe that today's provisional findings are good news for passengers and airlines.
We have consistently stated that the group [MAG] is interested in acquiring assets that will add value for our shareholders and this could include one or more of the BAA airports.
We are currently examining the details of today's report before making any decision about future acquisitions.
CIVIL AVIATION AUTHORITY
We note the commission's findings are broadly consistent with the key points made by the CAA in its submission to the CC in May.
They were that common ownership has an adverse effect on competition, that the planning regime has the potential adversely to affect competition, and that there is a need for reform of the current statutory regulatory regime.
STANSTED AIRLINE CONSULTATIVE COMMITTEE
The liberation of Stansted airport from the dead hand of the BAA monopoly will be a great first step in the recovery of UK aviation, which for far too long has suffered gross inefficiencies, long queues and high costs.
It is essential that competition within and between London airports is promoted, along with effective regulation, to the benefit of passengers, tourism and the economy.
On behalf of our 25 million customers at Stansted, we now hope that Stansted will at last listen to its customers by reversing their 100% price hike, eliminate long queues and build efficient facilities, which users actually need.
UNITE NATIONAL SECRETARY STEVE TURNER
Any attempt to break up BAA will be resisted. This union and our members will not sit back while the market plays games with their jobs and their terms and conditions of employment.
A break-up of the BAA would see economies of scale removed and many of the benefits to passengers of retail operations being lost. We see no benefit to our members or the travelling public from any break-up.
BRITISH CHAMBERS OF COMMERCE
We're supportive of measures which aim to improve the passenger experience.
Businesses are heavily reliant on air travel and at present, they are not receiving the level of service required. Increasing competition in the market is a key tool in improving this situation.
However, we must not lose sight of the need to maintain Heathrow as a global hub. The Commission's proposals must be considered in tandem with essential expansion at Heathrow.
DEPARTMENT FOR TRANSPORT
The government's role is to ensure a policy and regulatory framework that serves the interests of airport users and the public.
We remain committed to the outcome of the sustainable delivery of new airport capacity for the benefit of air transport users and the wider UK economy.
SHADOW TRANSPORT SECRETARY THERESA VILLIERS
BAA too often gives its customers, quite frankly, a dismal level of service.
All experience tells us that if companies are subjected to more competition and their customers are allowed to vote with their feet if they don't get a good level of service, then we see service quality improve.
So I think the Competition Commission is absolutely right.
LIB DEM TRANSPORT SPOKESMAN NORMAN BAKER
Today's decision is a victory for UK air passengers who have put up with a second-class service at what should be London's first-class airports.
Breaking up the BAA monopoly is a long-overdue move to make aviation fairer to passengers.