NHS staff are more than twice as likely as patients to be served fresh food in hospitals, according to a new report.
The Campaign for Better Hospital Food found that just 30% of London hospitals cooked food fresh on-site for patients, but 77% had canteens offering fresh food to staff.
Almost a fifth (17%) of hospitals also served food to patients in ready-meal packaging, the investigation found.
Furthermore, a fifth of hospitals fail to provide a hot meal for patients who miss a mealtime.
Half of the hospitals surveyed are also failing to meet basic standards for nutrition and hydration.
The campaign is now calling for tough new legal requirements for patient food similar to those in prisons and schools.
New Great British Bake Off judge Prue Leith, who is backing the campaign, has described hospital food as "inedible" and "foul-smelling sludge".
She said: "Hospital food has a deservedly poor reputation and NHS patients and staff deserve better.
"Our hope is that it will be obvious to Hospital Trusts and Government that if they mean to tackle poor catering standards, they will have to face up to some increased spending.
"A meal of good fresh ingredients prepared by skilled cooks might cost marginally more than a pre-frozen meal from a far-away factory."
Jo Ralling, Jamie Oliver Food Foundation campaign manager and supporter of the campaign, said: "We've had legal food standards for schools and prisons for a decade, there's no reason we can't extend these same protections to hospitals. Let's all work together to get NHS patients and staff the good healthy food they deserve."
Katherine Button, coordinator of the Campaign for Better Hospital Food, said: "The Government has failed to take seriously the dire state of hospital food for too long and now half of London hospitals are not meeting even basic food standards.
"Good food plays an essential role in recovery, well-being and morale, and patients and staff in NHS hospitals deserve better.
"The standard of food in schools and in prisons is protected by legal minimum standards and we demand the same high quality food for patients, staff and visitors eating in hospitals."