GlaxomSmithKline have made a $2.6 billion (£1.6 billion) bid for its long term partner, Human Genome Sciences. GSK, Britain’s biggest pharmaceuticals firm, made a bid worth $13 a share for HGS – 80% higher than the closing price last night.

However, HGS rejected the bid and have said they are considering putting themselves up for sale. The board said: “The offer does not reflect the value inherent in HGS... Its board has authorised the exploration of strategic alternatives in the best interests of shareholders, including, but not limited to, a potential sale of the company.”

GSK CEO Sir Andrew Witty said “Having worked together with Human Genome Sciences for nearly 20 years, we believe there is clear strategic and financial logic to this combination.”

HGS, the Us based biotechnology specialist, have worked with GSK on treatments including lupus medicine Benlysta.