A small group of NHS patients are adding to pressures on accident and emergency departments by going to casualty dozens of times a year, according to an investigation by the BBC.
Figures obtained under freedom of information legislation showed that almost 12,000 people made more than 10 visits to the same A&E unit in 2012/13, with just over 150 attending on more than 50 occasions.
In the most extreme cases, one patient at Luton and Dunstable Hospital went to casualty 234 times over the course of the year, while another person went to Sheffield's Northern General 223 times.
The BBC asked for information from 175 hospital trusts and boards across the UK on repeat attendances during 2012/13. A total of 106 responded, providing figures covering 183 units.
Dr Cliff Mann, of the College of Emergency Medicine, told the BBC: "At a time when emergency departments are very busy, it is clear that repeat non-emergency attendees are adding to the pressures."
In some cases, frequent visitors had mental health issues or problems with drug and alcohol abuse, which suggested that improved support in the community could reduce their use of A&E departments, he said.
A spokeswoman for NHS England said repeat attenders made up only a small proportion of the 21 million visits to A&E a year in England alone.
"The figures presented here suggest that the number of people attending A&E frequently is relatively small when considered against the big picture," said the spokeswoman.
"Our A&E departments are trusted by the public and it is really important that people know the NHS will be there for them if they need treatment and care."
But she added: "It is also important that patients and the public know about and use the full range of health services in their local area. The NHS works hard to ensure people know where to go to get the best care and can use services appropriately."
The figures showed that fewer than 12,000 people accounted for around 200,000 A&E visits over the course of the year.
Dr Mann told BBC Radio 4's Today programme: "The figures show that some individuals actually attended 250 times a year, which is almost five times a week, whereas other people are using it 10 times a year, which is more like once a month.
"There's clearly a difference between those groups, but most of them represent groups which are to some extent on the margins of society - a lot of problems associated with drugs and alcohol, some with homelessness, a lot with mental health problems, isolation and loneliness for some individuals.
"Also, with the news recently about migration, I think it's fair to say that people who are unfamiliar with the system of healthcare in this country, and in particular the way in which we access general practice, for many of those people - at least when they first arrive - attending an A&E department seems the most straightforward way to access healthcare."
Dr Mann said that the facilities and expertise available in A&E were often not suited to the needs of those making frequent visits, and efforts are made to redirect them to specialist services.
But he said: "Unfortunately, we are not able to guarantee them access to those other services. We don't have direct links, by and large, into mental health services, drug and alcohol services or even primary care out of hours.
"I think that the lack of integration around the margins of healthcare is a real problem and causes people to fall between two stools far too often.
"The problem is that many of these services are run as individual services without a real focus on those problems of integration."