London (dpa) - Due to problems checking in at at least three UK airports, thousands of British Airways passengers have to be patient. Affected were London's Heathrow, Gatwick and London City Airport. The exact extent of the problems in the middle of the summer holidays is still unclear, said an airline spokeswoman for the German Press Agency. British Airlines warned about short-term cancellations and delays at London airports. Short-haul flights from the affected airports could be rebooked to another day.