Every teenager knows that when they turn 17 they can sit their driving test.

But very few teenagers know that at 17 they can also donate blood for the first time.

Over the next few months, the Scottish National Blood Transfusion Service (SNBTS) aims to change that by visiting schools to encourage young people to sign up as donors. Two thousand have already done so since the beginning of the year, but more are needed.

If anyone needs reminding of the reasons, Sammi Bradley and Rachel Laird were on hand yesterday to relate their experiences. Both of them have been treated for leukaemia and relied on donated blood throughout. "I really relied on donations," said Rachel, who is 19 and from Edinburgh. "It saves your life."

During the treatment, some of Rachel's friends helped out by donating blood, but they are the exception rather than the rule - the average age of donors is 40.

The aim of the SNBTS campaign is to lower that average. With donors who sign up at 17 likely to continue donating, it could also help guarantee Scotland's blood supplies for many years to come.