Lafarge, the French cement group, has launched a huge €1.5bn ($1.3bn) convertible bond to help finance its £3.1bn (€5.1bn) acquisition of UK rival Blue Circle.

Selling the issue will be a challenge for bookrunners SG and Schroder Salomon Smith Barney (SSSB), as they are offering the deal at a fixed price and the underlying shares are falling. This means that the conversion premium is wider and so the bond looks more expensive.