Four-year-old Jessica Knight has an unusual appetite for furniture, soft furnishings and fittings, and doctors say they are unable to treat her.

Hardly anything is off the youngster’s menu, with the filling from a rocking horse, padding in an armchair and even carpet underlay taking her fancy.

Other non-food items she devours include sand and chips of cement from paving blocks.

Jessica suffers from pica, a rare medical disorder that leads to an appetite for non-nutritious substances. It is more commonly recognised among pregnant women, some of whom develop unusual cravings.

‘I was really shocked when I realised just how much she was eating. If you lift up the carpet in her room now you can see there is no underlay left,’ said her mother, Kelly Will. ‘We are at our wits’ end. We try to keep her busy so she doesn’t do it, but if we try to stop her she will find a way to do it.

‘I’d have to remove everything from my house, including all chairs and sofas.’ Miss Will, 36, first noticed the problem when Jessica was two and began eating the filling from a children’s armchair.

Staff at her pre-school also spotted her licking her hands and placing them in a sandpit before sucking the grains from her fingers, before tell-tale signs of snack-attacks became clear from the damage to items around the house.

Jessica is now allowed to keep a small purse filled with some of the spongy underlay to eat.

Her mother, who lives in March, Cambridgeshire, with partner Chris Knight, 40, an engineer, said: ‘We’d rather she ate the underlay because it is non-toxic. If we try and stop her we fear she will eat something with chemicals in it.’

Experts have examined Jessica but said they cannot intervene until she is six, and old enough to make conscious decisions about what she eats rather than acting on impulse.

Fortunately, she does like plain sausages, cheese strings, rice pudding, bread, Weetabix and fish fingers.

But her unusual snacks can leave her in agony because they cause stomach cramps and constipation.

Despite her tender years, Jessica is aware that her diet is highly unusual, and does worry what people would think of her craving different food. She also shuts her little sister out of their shared room when she is satisfying one of her cravings, saying: ‘I don’t want her to be poorly.’