The solution used to preserve most donor organs in the UK could be contaminated with bacteria, the government has said.
Viaspan preserves the kidney, liver, pancreas and bowel, and is often used when organs are transported around the country.
Tests in recent days have found the presence of a bacteria, Bacillus cereus, in the solution.
The manufacturer of Viaspan, Bristol-Myers Squibb, issued a recall of the product after tests on its production line revealed the bug.
The line was last tested in July. The company has said it cannot guarantee the safety of Viaspan since that date.
Hundreds of Britons have received organs since July, although transplant centres have reported no adverse effects in patients linked to possible contamination.
The government and the Medicines and Healthcare products Regulatory Agency (MHRA) are now working to secure alternative liquids.
Until then, Viaspan will still be used in the UK and patients can be prescribed an antibiotic in case the bug is present.
Chief Medical Officer, Professor Dame Sally Davies, said: "Our priority is to ensure patients are safe.
"There is currently no evidence of any problems in patients who have recently had transplants where Viaspan has been used.
"If we were to recall the product immediately it is clear that patients would suffer and some may die.
"The manufacturer has advised that, where necessary, Viaspan can continue to be used until transplant teams have stocks of alternative products and patients can be prescribed an antibiotic known to be effective against the contaminant as a precaution.
"Every day doctors and transplant teams make clinical decisions which weigh up the risks and benefits for their patients and they will continue to do so.
"We are now working urgently to source alternative products. The MHRA is working closely with the manufacturers and tests are ongoing."
Bacillus cereus is most well known for producing a toxin in food which causes food poisoning.
Symptoms of the poisoning include diarrhoea - which may be bloody and severe - nausea, vomiting and stomach cramps.
Last week the MHRA, which oversees the safety of medicines and devices, issued a warning to UK transplant centres about the bug.
It said the bacteria had been found in the solution used to test the sterility of Viaspan, but not in Viaspan itself.
However, the most recent tests on Viaspan have shown the bug to be present.
Professor Sir Kent Woods, chief executive of the MHRA, said: "There is no evidence from transplant centres that patients who have had transplants using this solution are experiencing any related healthcare problems.
"We have acted quickly to protect patients and we have alerted transplant centres and surgeons immediately about this contamination and precautionary recall by the manufacturer.
"We are working closely with the NHS to make alternative products available for transplant operations.
"We support the decision to use Viaspan if it is clinically appropriate for patients and there are no alternatives available.
"Situations like this are very rare. If transplant patients have any questions, they should speak to their doctor."
Lorna Williamson, NHS Blood and Transplant medical and research director, said: "NHSBT endorses the decision to continue to use Viaspan until suitable alternative products are available.
"This is necessary, if the transplant programme is not to be affected by this product recall.
"We are reassured that no adverse events have been reported related to this product.
"For patients suffering from terminal liver disease a transplant may be the only treatment and for many cannot be delayed even for a few days.
"NHSBT is working with the MHRA and the transplant centres to ensure that the vital transplant programme continues.
"We are liaising with the Department of Health over supplies of alternative products and are ready to offer transport assistance if needed."
A statement from Bristol-Myers Squibb said the firm took its responsibility for patient safety "extremely seriously".
It added: "We routinely monitor our manufacturing lines to confirm that our products conform to the highest quality standards required by the regulatory authorities.
"During one such routine test we received notification from the third-party manufacturer of potential contamination on the production line.
"Following this notification, we have taken the precautionary measure of recalling all batches of Viaspan.
"We are urgently investigating the cause of this issue, and our action to recall the product has been taken to safeguard patients in the UK from any unnecessary risk.
"BMS has notified all health authorities in countries where the product is distributed and will provide further updates as the investigation progresses.
"The recall will result in a temporary out of stock situation.
"As there are alternative solutions for organ preservation available within the UK, we recommend that transplantation centres source and use one of these alternatives until the investigation has been satisfactorily concluded and normal supply can be resumed."
One is Soltran (also known as Marshall's Solution), which is available in the UK.
Two further solutions - Celsior and HTK - have been identified to maintain the viability of pancreatic, liver and bowel transplants.
The department said neither has a kite mark in the UK for organ preservation.
However, last night the MHRA authorised both products for humanitarian use and is working to confirm their availability.