Credit Suisse First Boston and Société Générale will formally launch the multi-billion euro secondary sale of shares in Alstom, the French engineering group, on Thursday in what will be the biggest equity deal of the year so far in Europe.

According to banking sources in Paris, bookbuilding and a formal roadshow will kick off on Thursday morning. The sale is expected to raise between €1.4bn ($1.3bn) and €2.6bn. Alcatel, the French electronics group, and Marconi, its UK counterpart, announced at the beginning of January that they were planning to sell down some of their stakes. Each firm has 24% of Alstom from its IPO in 1998.