Pfizer yesterday increased its offer to AstraZeneca to £63 billion but the UK company rebuffed what it called a "tax-driven" structure.
Leif Johansson, chairman of AstraZeneca, said: "AstraZeneca continues to invest significantly in research, development and manufacturing in the UK, Sweden and the US
"We are showing strong momentum as an independent company, in particular with our exciting, rapidly progressing pipeline, which the board believes will deliver significant value for shareholders.
"Pfizer's proposal would dramatically dilute AstraZeneca shareholders' exposure to our unique pipeline and would create risks around its delivery."
While making much of its research base in the UK, AstraZeneca currently has little presence north of the Border after shutting its clinical research operation in Edinburgh in 2011. It retains a small sales, marketing and public affairs team in Scotland.
Mr Read studied chemical engineering at Imperial College, London before becoming an accountant under the auspices of the Institute of Chartered Accountants of England and Wales. He is now a US citizen.
Mr Read has sought to overcome worries that the UK could be downgraded in any combination by promising to complete a new research centre planned by AstraZeneca in Cambridge and retain a manufacturing plant in Macclesfield.
Analysts and investors have said that after being rebuffed for a second time, despite upping his offer from 4,661p to 5,000p a share, Mr Read might take his proposal, which would boost its pipeline of cancer drugs and create significant tax and cost savings, directly to AstraZeneca shareholders.
The US group would prefer an agreed deal, since hostile takeovers typically take longer, require a higher price and carry more risks because the bidder has less access to the books of its target.
Some analysts are convinced Pfizer will raise its offer again, because it will want to get the deal done before any change in US tax rules that might prevent it moving its tax base to Britain.
Pfizer's latest proposal would have seen investors receiving, for each AstraZeneca share, 1.845 shares in the combined company and 1598p in cash.
AstraZeneca's shares closed down 7p or 0.2% at 4808p.