Obtaining services by deception?
There is a long tradition of that in the pub. I'm sure I'm not the only one that lied about my age when I was 17.
People lie and cheat and aren't put off by potential sentences. They are influenced by perceived risk of being caught. I don't think the odds of being caught using a fake app or certificate in a pub are very high. Do you?
I'm half vaccinated and have my second shot booked so it doesn't really matter to me but I'm sure there are plenty of people that don't want to be vaccinated and would be prepared to cheat.