Under the deal Porton's management will take an initial 22 per cent stake in Speywood. Speywood said it had undertakings for 60.5 per cent of Porton's share capital to accept the offer of pounds 13.40 for each share.
Beaufour Ibsen had 1993 sales of Fr2.6bn ( pounds 322m), with non-French sales accounting for just over a third of the total.
Porton was one of the earliest biotechnology companies, specialising in haemophilia, oncology and neurology.
In 1985 it raised pounds 75m from several big institutional investors including Legal and General, Sun Alliance, Lloyds Bank and the pension funds of British Telecom, Imperial Chemical Industries and the Post Office, but its progress has been disappointing, with criticism of its lavish spending and secrecy.
In April it raised pounds 3.2m through the sale of Porton Cambridge, specialising in in- vitro diagnostic tests, to Shield Diagnostics.
The move was seen as a cupboard-clearing exercise before a sale. In March it had engaged the merchant bankers Kleinwort Benson to explore which pharmaceutical groups might be interested in buying it. The possibility of a stock market flotation was also investigated.
Meanwhile, Zeneca's Cellmark Diagnostics business has been appointed as exclusive European distributor for a new, more effective, product to detect Down's syndrome and other foetal chromosomal abnormalities. The test, GenSite, was developed by Aprogenex, of Houston, Texas.Reuse content