Asda has denied its decision to start dispensing privately-prescribed cancer drugs at not-for-profit prices is a publicity stunt.
Announcing the move last month, the retailer claimed patients could now save up to 76% if they brought their prescriptions to Asda.
It listed seven of the most commonly privately prescribed drugs and compared its prices against those of high-street and supermarket rivals.
One was leukaemia drug Tasigna, which it said would cost £2,432.85 for 30 days' supply at Asda, compared with £4,287.90 at Sainsbury's.
Although Sainsbury's Tesco, Boots and Superdrug promptly agreed to match the prices, rivals questioned how much demand there actually was for such drugs from a supermarket pharmacy.
Boots said it had no record of having dispensed any of the seven drugs Asda listed. "These drugs are more likely to be dispensed in a hospital by a consultant specialising in cancer care and they are very unlikely to be dispensed in a high-street setting," said Paul Bennett, professional standards director.
A Superdrug spokeswoman agreed: "It's very rare for community pharmacy to receive private prescriptions for these drugs."
A spokeswoman for Roche, which manufactures the pancreatic cancer treatment Tarceva one of the drugs Asda mentioned in its price comparison said she was not aware of the drug being dispensed by a pharmacist.
However, Asda insisted the drugs were available at Asda and its price pledge was a serious commitment. "One per cent of all anti-cancer drugs are supplied privately so it's not a big demand," a spokeswoman said.
"We can't give figures but since launch we've seen a 44% increase in people coming to us for privately prescribed anti-cancer treatments.
"Even if it helped 10 people afford lifesaving drugs it's worth it. It's not just a publicity stunt."
Asda to sell cancer drugs in not-for-profit move (21 May 2010)
Asda to sell cheap fertility drugs (3 March 2010)