Moral of the story - Concentrate on what you're doing + small Halford trolley jacks don't really have a big enough head for the job.
Still - at least I saved the labour on the brake-pads . Shame about the cost of the new engine sump though! (I hope I haven't damaged anything else!).
Just waiting for car to be towed to the dealer for repair now.
Did you want to add the step of - Let car fall off jack just before the make cup of tea?