We don't need to have it enshrined in law as right now little to no ISPs outright prevent access to popular services but as you said zero-rating is slowly creep

We don't need to have it enshrined in law as right now little to no ISPs outright prevent access to popular services but as you said zero-rating is slowly creeping in. Until an ISP starts preventing universal access nothing needs to be done, zero-rating (while bad for competition) does not do that. A good question would be why aren't the competition petitioning the government to outright ban zero-rating? Current EU law has zero-rating loopholes, it'd be up to a post-brexit government to close them. Perhaps it's not popular with current ISPs and their customers? I don't think a large survey on net neutrality has been done in the UK.