Whether the term is enforceable or not is debatable and almost certain to be rendered moot. Unlike US Republicans, UK Conservatives do actually believe in the rule of law and honest business practices (sort of). There isn't any party who believes that screwing the consumer is a constitutional right. There will be a bill passed.
A rather more direct question is whether the hotelier was entitled to collect the charge under the credit card agreement. And that is unambiguous, he isn't. A credit card merchant cannot use a charge card to recover a disputed charge. It does not matter what the purported contract term was or if it is enforceable. The credit card agreements are designed to prevent cardholders from dishonest merchants. So the consumer will get their refund and the hotelier will find themselves facing a 30 quid chargeback fee.
The only option for the hotelier to recover would be to take the matter to court. The most he could win is the hundred pounds, if he lost he would likely be out the legal costs which could be a couple of thousand. Small claims courts don't usually award costs but they might well do so in this case. Judges tend to detest bullies.