It takes around an hour to give blood but the benefits to both donors and patients are lasting.

Yet in Swindon, as in the rest of the country, attendances at donor sessions are down by 10 per cent and there are just three days of blood in stock instead of the five days needed in the run up to Christmas.

Much of this is due to the recent floods and severe weather which have made it difficult for regular and new donors to get to sessions. Bouts of flu have also prevented many donors from giving blood as they need to be healthy in order to donate.

And with the possibility of a second fuel crisis looming the situation could get worse.

The National Blood Service says it is "concerned" by the shortage and needs people to come forward now in order to prevent an emergency at Christmas.

"October and November are usually the two months we really rely on for building up stocks after the summer break and before Christmas. They are usually our two best months," said Annabel Bruxner-Randall, spokeswoman for the South West Area of the National Blood Service.

"But with half term and the floods last week along with flu, we have seen a down turn in attendance at donor sessions by more than 10 per cent.

"It is not the fault of donors because they were told to stay at home during the worst of the weather but we are urging anyone now who can get to a session to make the effort. We are also asking any regular donors who missed their usual session to go now as well rather than waiting for another four months until the next reminder letter comes through the door."

Blood donated has just 35 days shelf life so depleted stocks must be replenished very regularly. Across the country 10,000 units need to be collected each day.

It is vitally important for the Blood Service to build up stocks now because with so many bank holidays over Christmas it is very difficult for it to run sessions.

With so many other events going on over the festive period it is also very hard to recruit anyone to give blood.

"At Christmas time the pressures on people are phenomenal and the last thing people think about is giving blood," said Annabel. "But although the number of donors goes down and the number of sessions we hold, hospitals still work on the same basis and need just as much blood.

"It is a concern that we are running low. It is not an emergency situation but in order for us to be professional we need to address it now before it does become one."

As well as the problems with floods, flu and bank holidays there is one other factor which can lower the level of blood stocks.

Only six per cent of people who are eligible to donate actually do, mainly through fear that it will hurt or ignorance about the process.

In reality it is nothing more than a needle prick which can be made painless with a local anaesthetic and donors are monitored throughout to ensure they have no adverse reactions which very rarely happens.

People can donate three times a year at an interval of 16 or 17 weeks because it takes that amount of time to replace certain elements in the blood but donors feel fine after their donation as the body works very quickly to replenish blood it has lost.

Blood taken from people in sessions in Swindon goes to local hospitals within two days after it is sent to Bristol to be screened and tested and can help in the treatment of more than one patient as donations are divided into more than one product.

Annabel added: "Giving blood is such a good thing to do. Most of our donors say the sense of well-being afterwards is great.

"It is the chance for a regular health check for them and to do something to help someone in dire need of treatment.

"It really is saving a life."

Anyone who wants to become a donor can go along to a local session without an appointment.

To find out more information call the National Donor Helpline on 0345 711 711 or visit its website at www.blood.co.uk