* Mike Brown to leave BAA after just over a year
* Will head London Underground, where he worked for 18 years
LONDON, Sept 14 (Reuters) - Britain's Heathrow Airport chief Mike Brown is to leave his post at the country's biggest airport after just over a year to head up London Underground.
Airports operator BAA, majority owned by Spain's Ferrovial, said in a Monday statement Brown was leaving to become Managing Director of London Underground, where he worked for 18 years before joining Heathrow in May 2008.
"Mike will remain at Heathrow until March 2010 ... Our search for a successor has started," the company said.
Brown joined BAA after previous Heathrow boss Mark Bullock resigned in the wake of the botched opening of the new Terminal 5 building in March of that year.
The near 150-year old London Underground has been seeking a new head since Tim O'Toole resigned earlier this year to return to his native United States. (Reporting by John Bowker; Editing by Jon Loades-Carter)