To be fair, penalty clauses in contracts are unenforceable. That is pretty much a cast iron tenet of English contract law. However a clause which provides for a proportionate remedy in protection of a legitimate interest is unlikely to be deemed a penalty clause and will be enforceable. The government would have been able to draft an appropriate clause to protect itself, but chose not to for some reason...
What makes Boris more qualified than Corbyn? And this isn't a rerun of the election kind of question. What was the difference? What up until now can you Boris and his cabinet have achieved? Check out the front page of the Kentish Express, tells you all you need to know about how the oven ready deal Brexit is going.