The head of airport operator BAA is to step down after 18 months of misery at Heathrow and Gatwick, just as Heathrow’s Terminal 5 opens.

Chief executive Stephen Nelson will leave at the end of March and be replaced by former British Airways technical director and boss of Severn Trent water group Colin Matthews.

Nelson, a former BAA retail director and board member at supermarket group Sainsbury, only took over as chief executive following the takeover of BAA by Spanish group Ferrovial in June 2006.

Ferrovial has admitted it faces difficulties refinancing the £9 billion in debt incurred to buy BAA. The group is under investigation by the Competition Commission and the Civil Aviation Authority is shortly due to announce new price caps on landing charges at Heathrow and Gatwick. BAA has warned this could lead to cuts in investment.

The operator has been under severe pressure since a security alert in August 2006 lead to intensified security measures at airports, causing chaotic queues and delays.

Airlines accuse BAA of devoting more attention to providing designer shops than cutting queues. However, BAA denies this and argues the profits from its retail operations subsidise landing charges.

Terminal 5 is due to open on March 27 for the exclusive use of British Airways.