A mother whose young son ate a vital security component from her car key managed to press the child against the steering wheel and start the engine.

Amanda Webster, 34, of Summertown, Oxford, believed her Ford Focus had broken down during a shopping trip in west London. She called out the RAC thinking it might be an electrical problem.

But her son Oscar, one, had been playing with the keys and quick-thinking Keith Scott, an RAC patrol leader, realised Oscar might have swallowed the immobiliser chip.

The tiny security device, embedded in the key, emits a signal that is picked up close to the ignition.

Without the signal the car would not start.

Mr Scott said: "The initial call came in as a 'non-start' and I thought the car battery might be flat. But the lights worked, then I spotted the transmitter was missing from the keys."

Mrs Webster searched the car and her handbag then mentioned that her son had been playing with the keys and had had them in his mouth.

Mr Scott said: "I told her to put Oscar as close as she could to the steering wheel and, when she turned the key, the car started first time.

"I couldn't believe it, it was such a long shot. I was as surprised as Mrs Webster.

"Oscar thought it was really quite amusing he was still trying to play with the keys. I've spoken to her since and he's absolutely fine."

Mr Scott added: "It's something we'll have to put in our technical library.

"You never know when it could come in handy, so many strange things happen in this business."