Enforcement officers in the UK have seized a batch of Roche’s influenza drug Tamiflu that they believe has been stolen and offered for sale on the Internet.

The investigators, from the Medicines and Healthcare products Regulatory Agency (MHRA) carried out a raid at a London address and found 5,000 packs of Tamiflu (oseltamivir) with an estimated value of half a million pounds sterling.

The seizure comes at a time when Roche is racing to meet surging demand for Tamiflu as governments around the world - and individuals - are stockpiling the drug in anticipation of a flu pandemic. The current news of an outbreak of bird flu in Turkey, and several deaths, have exacerbated fears among consumers in Europe.

The MHRA said it believed the drug was genuine rather than counterfeit, but that testing to make sure would take a couple of weeks.

There have been a number of cases in which fake Tamiflu has been intercepted around the world in recent months, as crominals try to cash in on public fears of a pandemic. Just last week, US Customs and Border Protection officers seized 250 parcels of counterfeit Tamiflu being shipped into New York City.

Historically, flu pandemics have hit every few decades, killing millions around the world. The worst outbreak of the 20th century came in 1918-1919, where the strain known as Spanish flu caused 40-50 million deaths worldwide. Less serious outbreaks occurred in 1957-8 (Asian flu) and 1968-9 (Hong Kong flu), but since then there have been none, leading to speculation that the next outbreak is just around the corner.