When there are multiple potential defendants to a case, who should be sued? If you serve selectively against only one, and fail, your client loses the opportunity to gain any damages. Or the chosen defendant may succeed in arguing that it should only be partially liable for an injury, perhaps on the basis that it is a divisible injury, or that the chain of causation has been broken by subsequent actions, resulting in only partial recovery of damages for your client. If you bring proceedings against too many defendants, the consequences can be equally serious. If you succeed against only one, then you are at risk of adverse costs order(s) in favour of the other(s) that could wipe out your hard won damages. Moreover, discontinuance will trigger automatic costs orders.
In any case involving arguable claims against a number of potential defendants, careful consideration needs to be given to choosing the correct defendant(s) and whether bringing proceedings against multiple defendants is an advantageous or reasonable thing to do. The factors that need to be considered include potential legal liability (including questions of the merits of the case against each defendant, vicarious liability, non-delegable duties and whether the chain of causation has been broken), the damage suffered by the claimant (including whether it is divisible or indivisible), whether the defendant(s) are insured, costs implications (including proportionality), and any number of factors particular to the case.
Hannah Godfrey and Linda Jacobs have considered the issues and potential pitfalls of multiple defendant cases in detail in a recent paper, presented at the 2014 Cloisters Clinical Negligence & Personal Injury Seminar Series, which can be accessed by clicking the following link updated-final-handout-who-to-sue-2.docx.