More trouble with environmental experts

In 1996, there was a devastating flood in part of the City of Ottawa. A number of residents sued the City, alleging that its storm water drainage system was inadequate. The City retained Robert Bishop of MMM as its expert witness. Bishop  reported that the drainage system in the area met all applicable standards. The City settled the lawsuit, and decided not to make any changes to the drainage system.
Six years later, there was a second flood, and neighbours commenced a class-action. This time, the City retained a different consultant, who reported that the drainage system did not meet 1996 standards, and should definitely have been upgraded after the first flood. The City therefore wants to sue Bishop and MMM for anything it may have to pay in the class-action, i.e. add them as third parties.
Last month, in Robinson v. City of Ottawa,  the Superior Court held that they can. Bishop and MMM argued that they were immune from suit because they were hired as expert witnesses. The court decided that this is not necessarily so,  although a specific liability protection might have been included in the retainer agreement between Bishop and the City. Accordingly, the City can add its third-party claim against Bishop and MMM to the ongoing class action.