Two children and a man died in Britain on Monday after contracting swine flu although all had pre-existing health conditions, officials said.
The deaths of a man and a child from West Yorkshire in northern England and a nine-year-old child from London took the death toll from the virus in Britain to seven.
All had "underlying health issues", health officials said, without giving details of their conditions.
England's chief medical officer has said people with breathing problems and obese people are at high risk.
Health officials said they could not confirm whether swine flu or the pre-existing condition was the cause of death in either case in West Yorkshire.
Speaking about the child, a spokesman said: "At this stage, we have no confirmation whether or not swine flu was the cause of death."
In London, the National Health Service (NHS) said the nine-year-old child, whose gender was not identified, also had "serious underlying health problems".
The government warned last week that Britain could soon face more than 100,000 daily cases of swine flu if the current rate of infection is maintained.
Health officials have abandoned efforts to contain the virus, given the high number of cases, and have switched to focusing on treating infected people who fall into a high-risk group.
People who present the symptoms of swine flu are now given antiviral drugs without laboratory testing to confirm the presence of the virus.
Britain already has Europe's highest number of reported cases with nearly 7,500.
Latest figures released on Monday by the World Health Organization showed that swine flu had now affected almost 95,000 people in more than 130 countries and territories.