“First the court has to determine whether the claimant’s conduct was an abuse of process. Secondly, if it was, the court has to exercise its discretion as to whether or not to strike out the claim. It is at that second stage that the usual balancing exercise, and in particular considerations of proportionality, becomes relevant.”
“in a case like this (where the striking-out is based on the nature of the pleading, not a failure to comply with an order), there is no difference between the test to be applied by the court under the two rules”