Paul Drayson, the controversial Labour Party donor, is set to walk away from PowderJect, the vaccines company he founded a decade ago, with a windfall of more than £100m.
Mr Drayson agreed to sell the company, which has made a stockpile of smallpox vaccine for the UK's bioterrorist defences, to Chiron, a US-based vaccines specialist. The 550p-a-share deal, which took place yesterday, values PowderJect at £542m, more than the market had been expecting.
Together with the stakes held by his wife and father-in-law, Mr Drayson controls almost 20 per cent of the company, and has agreed to sell these shares to Chiron.
Analysts said a counter-bid looks unlikely, and shareholders will not now be paid the 3p final dividend which was declared - for the first time ever - by PowderJect just last week.
Mr Drayson will leave the company if shareholders agree the deal, but said he did not yet have plans for another business venture. "I am 47 and I certainly don't see myself retiring to sit on the beach. I will want to do something, although I haven't had time to give thought yet to what that something might be."
Chiron wants to get its hands on PowderJect's flu vaccine, Fluvirin, to give it access to the growing US market for flu jabs. The majority of Chiron's sales are currently in Europe.
John Lambert, Chiron's vaccines chief, said: "The demand for flu vaccine far exceeds supply. In the US, there is only PowderJect and one other player in the market."
Chiron first made its desire to acquire PowderJect known last autumn, but talks broke down when the US company refused to bid more than 500p a share. Mr Lambert said that several things made PowderJect more attractive barely six months later, because a third flu vaccine maker had quit the US market and because the US is now recommending all over-50s are given a flu jab every year.
The takeover brings the curtain down on a stormy six-year period as a stock market-listed company. PowderJect was originally conceived as a vehicle for developing a needle-free injection device invented by Mr Drayson's father-in-law, Professor Brian Bellhouse.
Although that device is still being tested, the company moved into profit through a string of acquisitions which turned it into one of Europe's largest vaccines companies. Last week it posted an annual profit of £23.5m.
Some in the City expressed dismay that the UK's most prestigious vaccines plant had fallen into foreign ownership, but Chiron insisted it would keep the facility in Speke near Liverpool.