Private equity firm Bain Capital has bought a majority stake in the Government-owned blood products company Plasma Resources UK.
Bain Capital is understood to be buying an 80% stake in the company, with the Government - which announced plans to sell it in January - keeping the rest.
In a written ministerial statement, Health Minister Dr Dan Poulter said: "We are taking this action to support the company and its employees in the next phase of the company's development."
He continued: "We have carefully examined the strategic options that will best allow the company (which includes the UK based fractionation facility Bio Products Laboratory Limited (BPL) and the US-based plasma supply company, DCI Biologicals Inc) to grow and be successful in an established and highly competitive global industry.
"It should fulfil its potential as part of the strategically important bioscience sector of the UK economy. Our conclusion is that this route will best meet those requirements."
Former health minister Lord Owen heavily criticised the deal, asking: "Is there no limit to what and how this coalition government will privatise?"
He told The Independent: "It's hard to conceive of a worse outcome for a sale of this particularly sensitive national health asset than a private equity company with none of the safeguards in terms of governance of a publicly quoted company and being answerable to shareholders.
"Private equity has a useful function, as I saw in years past on the advisory board of Terra Firma, but Bain Capital should not have been chosen for this sale."
Plasma is a straw-coloured, clear liquid made up of 90% water. It carries blood cells around the body, making it an essential ingredient for human survival.
Plasma Resources UK turns plasma into life-saving treatments for immune deficiencies, neurological diseases and haemophilia.