You are relatively accurate with your assumptions, but the devil is in the details.
If you fail a module, but manage to score over 30%, then you will be entitled to a capped resit. The downside to this is that your final result will be capped at a Pass 4, unless you submitted a special circumstances form on time and they decide not to cap the resit.
If you score less than 30%, that is an outright fail and you will need to retake the module (or pick another one if you prefer). You will not have to start your degree over from scratch!
Because resits are capped, you might want to think strategically. It does not matter so much for level 1 modules, but from level 2 upwards, they do count towards your degree classification. If this is a module that counts, it might be a good idea to reassess your progress closer to exam time. If you are certain that you cannot pass, then it might be better to defer the module before the exam so that you have a chance to retake it and get better results. That will also provide you with a 25% deferral credit which you can use towards the cost of your next module.