The NHS has launched an urgent appeal for blood donors to prevent a potential crisis in supplies this summer.
NHS Blood and Transplant says it needs to boost stocks to 30% above usual levels to cope with the expected 1.2 million Olympic visitors from abroad.
But the run up to the Games includes the Jubilee celebrations and the Euro football championships, events that could lead donations to slump by 20%.
Assistant director for blood collection Jon Latham told Sky News: "We have got a lot of evidence that during sporting events the collection of blood is harder.
"People get distracted doing other things and don't make their appointments. We want to collect blood before the Olympics so during that period people can just enjoy the Games."
In the build up to the Games there will be more appointments in collection clinics, longer opening hours and - the service hopes - more new donors.
Currently, just 4% of people who could donate blood actually do so.
The NHS needs 7,000 units of blood each day to treat cancer, trauma, and complications from operations and childbirth.
Each unit saves or improves the lives of three patients.
David Copes suffered 41 fractures and serious internal injuries when a van pulled out in front of his motorbike. His life was saved by a massive transfusion.
"I owe my life to 40 total strangers," he said.
"I needed 40 pints of blood in the first few hours. And if there hadn't been 40 people donating blood I wouldn't be here. I would have died on the tarmac."
Appointments to donate blood can be made at www.blood.co.uk or on 0300 123 23 23 .