There was opposition in parliament, though. It was only passed because they snuck it in while MPs had left for summer vacation, and the parliamentary rules are absolutely pants-on-head idiotic and default to passing proposed legislation if a majority of all MPs do not vote it down (rather than merely the ones present). In other words, they passed it by default without achieving any kind of majority, because there weren't enough people physically present to vote it down.

The EU never delegitimised itself more than it did with that act. Actively undermining parliament to knowingly impose legislation the population absolutely does not want validated every concern anti-EU advocates ever had.