The main effect will be that the embarrassment probably causes Britain to revise its libel laws to be more similar to the American system (which is much less favorable to the plaintiff).
Holocaust denial won't become more respectable (deniers will cite the court case, but it won't convince anyone who wasn't already convinced). Publishers will be more reluctant to publish books on the Holocaust in the UK (probably the most significant negative effect). Irving will end up with a substantial pot of money, but will still be reviled by most historians, they'll just be quieter about it. I assume Lipstadt's employer would pay her share of any judgement, and Penguin is big enough to survive.