Who can give blood?

Generally if you're fit and healthy, between 17 and 65 and you weigh over seven stone 12lbs (about 50kg), you should be able to donate.

You can't donate blood if you have:

• The flu, an active cold sore or are on antibiotics
• Syphilis, HIV, hepatitis B or C, HTVL (Human T-lymphotropic virus) or jaundice
• Had a tattoo, or other cosmetic treatment involving skin piercing in the last six months
• Had a blood transfusion since 1980, to protect against transmitting vCJD (variant creutzfeldt-jakob disease)
• Injected yourself with drugs
• Had gay sex with a male in the past 12 months (even with a condom)

You also shouldn't give blood if you are pregnant or have recently given birth. If you have travelled abroad to a malaria-risk area, you should wait six months before donating; you may not be able to give blood if you've recently had certain immunisations.

A few other restrictions apply so it's a good idea to check on the National Blood Service's website before you go to donate or call their helpline on 08457 711 711.

What will happen on the day?

"Giving blood is a relatively simple process and will take about an hour," says Craig Taylor from NHS Blood & Transplant. All you need to do is:

• Fill in a questionnaire: to make sure you and your blood are suitable for donation;
• Get your iron levels tested: to check you're not anaemic
• Donation time: Then it's onto the bed to give your donation, which shouldn't take more than five or ten minutes
• Tea and biscuits: Well done, the hard part's over and now it's time to relax with a cup of tea and a digestive, to allow your blood sugar levels recover

Giving blood shouldn't hurt and each donation takes about 470ml of blood (just under a pint), which your body quickly makes up, so you shouldn't feel any negative effects after donating.

Where can you give blood?

You can give blood every 16 weeks (roughly every four months). The National Blood Service holds over 23,000 sessions a year in various halls and buildings all over the country. They also have blood mobiles that go to companies so you can donate at work.

If you live in England or North Wales, check out the National Blood Service's website to find a local session convenient for you. Similar services exist in Scotland, Wales and Northern Ireland so wherever you are in the UK, it should be easy to donate.

"I first gave blood at 17," says Tamara. "I give blood because it saves lives especially as my blood type is A+, which is quite rare. A blood mobile regularly comes to my workplace. It's a great excuse to get away from your desk. There's nothing to worry about, the nurses and medical staff take great care of you and the discomfort is minimal compared to what you're doing to help."

Where does my blood go?

After donation, your blood will be separated into its various components, such as red cells, platelets and plasma, which could potentially save three different lives.

At the moment, only 4% of the eligible population give blood and although there isn't currently a national shortage, it's still important that more people donate. "We use 7,000 units of blood every day in England and North Wales, so we have to match the amount of supply with the ongoing demand," says Craig.

Hayley Smith, 22, suffers from diamond blackfan anaemia and needs blood transfusions every six weeks. "I don't make any red blood cells, so without the transfusions I'd be bedridden. But with them, I can go to work, go shopping and do the things that normal 22 year-olds do," says Hayley. "I'm really grateful to the blood donors who take time out of their day to give something so precious."

Are there any risks?

It's important to eat and drink something before you donate, otherwise you might feel faint. If you smoke, it's probably best to give it a miss for a couple of hours after, as it could make you feel dizzy. You may get some slight bruising, but that should soon disappear.

If you do feel faint after donating:

• Sit down and place your head between your knees
• Don't do any strenuous activity (an hour on the PlayStation should be fine - you've earned it)!
• Make sure you drink lots of liquid (but not booze) and eat some food
• If it persists, call the National Blood Service helpline on 08457 711 711 to get further advice

"Most people spend an hour of their day on Facebook or shopping, but in that hour you can potentially save up to three people's lives," says Hayley. "I'd like to say thank you to all the people who donate, and all those who would consider donating. You keep me alive."

Updated: 07/11/2011

Written by Marcella Carnevale