1. Apparatus for redirecting messages in a publish/subscribe messaging system, the apparatus being operable to: receive a first message for publication on a target message topic, the first message comprising a predetermined message element indicating that the first message comprises an instruction to redirect messages for a source message topic to the target message topic; record the first message; in response to receipt of a second message for publication on the source message topic, identify any recorded message comprising an instruction to redirect messages for the source message topic to a target message topic; and if any instruction to redirect messages for the source message topic is identified, then redirect the second message to the target message topic in the identified instruction.