Vote: Should visiting hours for hospital patients with dementia be more open?
The call from the National Federation of Women's Institutes (NFWI) comes after its latest report, which concluded that dementia patients are "suffering unnecessarily" while being cared for in hospitals across England and Wales.
A survey of 250 dementia carers found that just 38% said they were able to visit their loved one outside of normal visiting hours.
Only a quarter (26%) said they were given unrestricted access.
In its report, the NFWI said that a number of hospitals have extended their visiting hours and introduced measures to improve support for carers.
But it called for all hospital providers in England and local health boards in Wales to make it easier for carers to stay with their loved one outside of visiting hours.
The NFWI also urged health officials to roll out a "carer passport" scheme across every hospital.
The report's authors added that such schemes should offer flexible or open visiting hours, enabling carers to assist at mealtimes.
The poll also found that 37% of dementia patients were reported to have lost weight, 27% became dehydrated and 15% became malnourished while in hospital.
Lynne Stubbings, NFWI chairwoman, said: "These deeply concerning findings show an urgent need for further action. Too many carers are experiencing their loved ones suffering unnecessarily as a result of poor dementia care and a lack of willingness on the part of hospital staff to engage with them."
Gavin Terry, policy manager at the Alzheimer's Society, said: "Poor hospital care can have devastating consequences for someone with dementia - often staying longer in hospital than people without dementia.
"We have heard of people with dementia falling in hospital and suffering serious injuries because they weren't helped to the toilet, or starving because they couldn't communicate they were hungry."
A Welsh Government spokesman said: "Last month, we launched a new Dementia Action Plan to ensure people with dementia can live as independently as possible in their communities, helping to avoid unnecessary admissions to hospital or residential care and delays when someone is due to be discharged from care.
"Supported by an extra £10 million a year, it aims to create new ways of caring, training and increasing the number of support workers, increasing rates of diagnoses and strengthening collaborative working between social care and housing."