They no longer use plasma collected from british donors to make the various plasma =derived products. Have not done for some while now, because of the risk of vCJD.
That is why BPL, or rather its holding company, bought a chain of US blood and plasma collection centres across the US. All donors in the US are paid for their donation.
http://www.bpl.co.uk/about-plasma/
So whilst I think it a huge error to sell to Bain Equity, I do not have a particular objection to the company be privatised. Ever since parts of the NHS was marketised, BPL have had an odd commercial role to play.
Second.
jakep commented on hospitals paying the blood transfusion service, or NHSBT, for blood and blood products for years. This is true - but again it came about as a consequence of the internal market created within the NHS. Rather than funds being disbursed to the NHSBT to collect and process blood products, each hospital was given a blood products budget instead, and units of blood were assigned a cost.
Its just another form of moving money around within the NHS. No commercial gain is involved. Currently, I think a unit of blood is costed at around £80 - there or thereabouts....