" ... first the judgment of the foreign court must be: (a) of a court of competent jurisdiction in relation to the party who is to be estopped (b) final and conclusive and (c) on the merits; secondly, the parties to the English litigation must be the same parties as in the foreign litigation; and, thirdly, the issues raised must be identical. A decision on the issue must have been necessary for the decision of the foreign court and not merely collateral."