Patients are being urged to inform hospital staff that they want to be visited by Jewish chaplains, following a toughening up of how data protection is enforced by NHS trusts.
Rebbetzin Rochel Ehrentreu, who has conducted visits at the Royal Free Hospital in north London for 30 years, complained that it was becoming increasingly difficult to gain access to patients.
Mrs Ehrentreu said she used to see around 25 patients a week but that number had declined to eight or less.
She added that teenage volunteers who conducted Shabbat visits were also finding it difficult.
The visits are particularly important to patients without family or friends.
Although the Data Protection Act has been in force for 15 years, Mrs Ehrentreu said that staff had still been willing to provide a list of Jewish patients. But the practice had now stopped.
The only way she knows if patients are Jewish, and might want to be visited, is if they have stated their religion on their admission form.
A spokeswoman for the Royal Free said it was hospital policy not to disclose any personal information to volunteers or visitors without their permission. "This includes information about their faith".
Mrs Ehrentreu said Jewish patients tended not to specifically ask for a visit, but were usually grateful if they received one.
"I'm not allowed to ask staff if there is anyone who would like a specifically Jewish visit. I meet people who say 'why didn't you come and visit', but we don't know they are there," she said. "I've been 30 years in the Royal Free and I know as soon as I come into the room if a patient doesn't want a visitor and I leave them."
She said her impression was that enforcement of data protection rules varies between hospital trusts.
Rabbi Yisroel Fine, chaplain to Barnet and Chase Farm Hospital, said that "each hospital exercises discretion and some are more rigorous".
He said that at Barnet, patients were asked about religious status and whether they would want a visitor, but that the system sometimes broke down because forms were not fully completed due to time constraints.
"We rely on goodwill of the staff. They are very co-operative, but the restrictions on data protection mean they have little room for manoeuvre."
Menachem Prager, a longstanding visitor at Edgware Community Hospital, said that the chaplaincy had "a wonderful relationship" with hospital officials.
Michelle Minsky, head of US Chesed, which co-ordinates hospital visits for Jews of all denominations, said the US was looking into working with other faith groups to bring up the matter with the Department of Health.
"We are finding this to be an increasing problem," she said. "More hospitals are affected."
"I want the wider community to be aware that they should make contact," said Mrs Ehrentreu. "You can't imagine what good visits do for people."
"I've tried anything because it hurts me that people are in hospital who we could be helping and we can't."
The spokeswoman for the Royal Free said: "A Shabbat room is available for patients and relatives who may be in hospital during the Sabbath.
"There are a number of Jewish volunteers, working under the supervision of our Chaplaincy and spiritual care team who are available should patients request to see them."
