Drop in number of young blood donors
Experts are worried about a generation gap in blood donors as figures show a 20% drop in the number of young people giving blood during the past decade.
There were 297,539 donors aged 17 to 34 in 2001, and now there are 237,520.
Research by NHS Blood and Transplant (NHSBT) suggests many young people are either too busy or daunted to donate.
Only 4% of eligible donors give blood, and most of these are above the age of 40. Just 14% of those who donate regularly are aged below 30.
The poll, of more 1,700 people across the country and 1,000 current NHSBT donors, suggests fear and ignorance, as well as time pressures, may be to blame.
One in 10 young people aged 18 to 24 said they were too busy, even though nearly three-quarters said everyone who met blood-donation criteria should give blood.
More than a third of the 184 people falling into the "young" age bracket said they did not donate because they had a fear of needles, while about a fifth said it was because they did not know where to go.
NHSBT is also concerned many blood donors fail to give on a regular basis.
About 200,000 blood donors of all ages drop off the register every year.
NHSBT assistant director of blood donation Jon Latham said: "We want to remind everyone that blood donation is one of the simplest ways you can save or improve a life - just one unit of blood can save the life of three adults or seven babies, and you can start donating from the age of 17."
The NHS needs 7,000 voluntary donations of blood every day to care for its patients.
The call for donors comes as organisers of the UK's biggest gay pride parade called for the ban on gay men giving blood to be lifted, saying it was based on "outdated stereotypes which are not fit for purpose".
Experts from the Advisory Committee on the Safety of Blood, Tissues and Organs have been reviewing the ban and are expected to advise ministers on the issue soon.