Drug group Pfizer has stepped up the pressure on rival AstraZeneca to accept its 63bn pounds bid for the UK pharmaceutical company.Pfizer issued a statement to the London Stock Exchange on Wednesday morning emphasising the benefits of a potential tie-up between the pair.AstraZeneca has so far refused to enter talks with Pfizer, saying its bid significantly undervalued the British company.Pfizer said it believed the merger would allow the two companies to deepen their research efforts and boost science innovation.It also said they could speed up development of treatments in areas such as cancer, immunology and inflammation, cardiovascular and metabolism and vaccines as well as expanding activities in emerging markets.Pfizer Chief Executive and Chairman Ian Read reiterated his belief that the tie-up could boost both companies."A combined company would bring together powerful and world leading research expertise in key therapeutic areas in which the world-class academic research resources in the 'golden triangle' of Oxford, Cambridge and London would represent a vital component," he said.There has been speculation that Pfizer could take its offer directly to shareholders if AstraZeneca continues to decline talks.Some of AstraZeneca's shareholders are thought to be unhappy that it has not consulted them and have pressed it to involve them in the discussions.Meanwhile on Wednesday, UK Business Secretary Vince Cable told lawmakers the government would not let Pfizer "use the UK as a tax haven".He pledged to secure British science jobs, possibly by extending public interest test powers to address any concerns about jobs or research and development investment.His comments came after the opposition Labour Party said an independent assessment of any potential deal was needed to safeguard the UK's scientific research base.PW