A breakdown company said that more than 20,000 motorists approached the firm for help to solve car key problems during 2009.
According to the Green Flag, the cold snap at the end of last year was behind the large numbers of cases of keys either breaking or getting stuck in cars' locks.
The top most reason for a key-related call-out was motorists locking their keys in the car. It was followed by keys jammed in locks, lost, broken, snapped and stolen keys.
Dan Robinson, head of Green Flag, said: "Locking keys in the car is not only frustrating, it can be dangerous too. Young children can often find themselves inside the car with parents or guardians looking in, hoping they don't nudge the handbrake or get hurt."
Mr Robinson continued: "After locking your keys in the car, the next most common key call-out is jammed keys in the ignition barrel or locks. December saw the highest volume of keys broken or snapped.
He added: "It is important you don't force your key into the barrel if the lock is iced over or feels stiff."
© Press Association 2010