OXFORD - Shire Pharmaceuticals Group plc today was to announce plans to merge with Roberts Pharmaceutical Corp. of the U.S. in a tax-free exchange of shares valued at about $1 billion.

Based on Friday's $27 closing price of Shire's American Depositary Shares, the proposed merger would create a company with a pro forma market capitalization of some $2.4 billion (£1.5 billion), and provide the British company with the acquisition news that The City has been seeking.