Its a witchhunt driven by people who dont fully understand the challenges of missile testing. The Russians average a 50% fail rate on their Bulava Missile (SLBM) which is at 12 tests failed from 24. The Americans historically design their missiles for a 90% success rate (stats elsewhere) but every single American programme has had as a percentage a far larger failure rate.
Missiles should work, but sometimes they don't. On this occasion it seems like it didnt but thats one of those things. Saying people will think the UK is a laughing stock or doesnt have a credible deterrent only makes sense sense if you apply exactly the same logic to the US, French, Russians who have all had identical problems.