Constitutionality is frought with difficulty. An application was brought before the Irish Supreme Court to take a case challenging the constitutionality of lockdown legislation. It was rejected on the basis that the applicants hadn’t made a case that the legislation was unconstitutional but “Rather, the attack on the regulations was based on the view of the applicants that the restrictions in question were disproportionate.” See link. That might seem like it was rejected out of hand but people who oppose the lockdown and think it is unconstitutional should be grateful to, rather than angry at, Justice Meenan for not hearing this case, because it would not have succeeded for the reasons outlined. They’d be better off finding a good lawyer and identifying actual reasons why the legislation is unconstitutional.
Personally, I actually think that a Supreme Court ruling on the matter would be helpful whichever way the ruling goes. The problem with proportionality is that is more a political matter than a constitutional one. I also think it would be easy for both the UK and Irish governments to argue that their legislation was proportionate.